Theresa Cassidy

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This page is about the Phase 2 incarnation of the character. For other uses, see Theresa Cassidy (disambiguation).

Theresa Cassidy
Portrayed by Holland Roden
Codename: Banshee
Affiliations: n/a
Birthdate: October 7, 1986
Journal: xp_banshee
Player: Cai

She's redheaded, five feet three inches tall, and feisty as fuck.


Character Journal: xp_banshee

Real Name: Theresa Maeve Cassidy-Rourke

Codename: Banshee

Aliases: Terry, Terry-Mae, Reese, Teresa/Tracy Rourke, Mae, Cass

First Appearance: December 8, 2018

Date of Birth: October 7, 1986

Place of Birth: Cassidy Keep in Enniskillen, County Fermanagh, Northern Ireland

Citizenship: Irish/UK

Relatives: Sean Cassidy (biological father), Maeve Cassidy (nee Rourke) (mother, deceased), Thomas "Black Tom" Cassidy (paternal uncle, "adoptive father"), Patrick Rourke (maternal grandfather).

Education: Graduated from Loreto Grammar School in Omagh, County Tyrone in 2004. Attended Oxford University, earning her BA in Philosophy, Politics, & Economics before going on to earn an MPhil, followed by a DPhil, in International Relations (also from Oxford).

Relationship Status: Dating Kyle Gibney.

Occupation: Former fundraiser for Médecins Sans Frontières, currently fundraising for the Muir Island Research Facility and the Xavier Institute. On the D/L, she forwards money and other items of interest (food, clothing, other basic necessities) to the Underground in New York State.

Team Affiliation: n/a



Shortly after her conception, Terry's father Sean was sent on an undercover, anti-terrorism mission by Interpol, its duration unknown. Terry was born in October of 1986, but her father was still undercover. Her paternal uncle Tom stepped in and helped her mother to maintain the family home. Unbeknownst to Maeve, Tom was heavily involved in the PIRA (Provisional Irish Republican Army) and had been working with them on a few 'special projects.' Unbeknownst to the PIRA, Tom was working on a few very 'special projects' of his own.

On November 8, 1987, just a month after Terry's first birthday, a bomb went off at Enniskillen's Remembrance Sunday ceremony. Tom had helped to plan the explosion targeting the British soldiers parading toward the ceremony — instead, the bomb went off near the town's war memorial, killing eleven civilians, amongst them Terry's mother, and one police officer. Tom, who'd vied with his brother Sean for Maeve's affections before she married Sean, tried to save her and Terry when he realized what had happened. Maeve had taken the brunt of the blast, shielding Terry with her own body, and she succumbed to her injuries shortly after Tom found them.

Tom knew that there was a good chance that Terry would be a mutant, given what he knew about his own family's penchant for powers, and he hoped he'd be able to utilize his niece's potential abilities at some point in the future. So, also knowing that he would be hunted by the PIRA, the loyalists, and the British because of the mistake that'd been made with the bomb's timer, Tom fled to County Mayo with Terry. There, he settled in Coolaba, just outside the Tullaghan Bay & Bog, and raised his niece — calling her his daughter — by himself until her maternal grandfather tracked them down in 1995.

Patrick Rourke was the last of his family in Enniskillen after his wife passed, and he'd heard through several different information pipelines that Tom Cassidy was up to no good in County Mayo with a young, redheaded girl that everyone knew as his daughter. The child apparently bore a striking resemblance to Patrick's daughter, Maeve, which piqued his interest — and his suspicions.

He and his wife had assumed that their granddaughter died at the war memorial with her mother, even though no body was found — she was small, at the time, and very close to the epicenter of the blast. Sean didn't return home from his undercover mission until nearly two years after it began, meaning that Maeve and Terry were already gone when he got back in 1988. Rather than add to Sean's grief by telling him of the daughter he'd never known and lost along with his beloved wife, the Rourkes kept the knowledge of Terry's birth and alleged death to themselves.

Strong words were had between Tom and Patrick, as well as threats of legal intervention and a final ultimatum: Tom would let Patrick leave with Terry — unchallenged — or Patrick would tell Sean Cassidy where his brother had run off to and who he'd taken with him. Tom folded quickly, knowing that any further prying into his business in Coolaba would reveal his network of criminal connections, as well as his involvement in the Remembrance Day bombing. At nine years old, Terry was scared by the angry discussions she overheard, unsure who this old man was and why he was there. She was even more frightened when her 'da' told her that she was going to have to go with the old man she didn't know to a place she'd never been — and that he wasn't actually her da. Patrick Rourke took his granddaughter back to Enniskillen during the winter of 1995, arriving home just in time for a Christmas reunion with her biological father. Needless to say, the holiday was filled with tension and disappointment, anger and frustration. Sean was upset with Patrick for not telling him of his daughter earlier, Patrick was tired of repeating his reasons for keeping Terry' existence a secret, Terry was hurt and traumatized after being so unceremoniously taken from the only family she'd ever known and finding out that the man she'd thought to be her da had been lying to her for her whole life. A new father couldn't take her da's place — not even when her da was a morally grey kidnapper and liar. All the presents on Christmas morning couldn't make up for the fact that she wasn't at home, where she wanted to be. A refurbished room in Cassidy Keep would never hold a candle to the one she'd grown up in and would never see again.

It wasn't until several months into 1996 that Terry began to open up to her new family members. Her relationship with Sean remained strained, mostly because she looked like a young Maeve, but also because she was wary of him. He still worked for Interpol, so he was often out of the country, putting further stress on their tenuous connection. She became closer to her grandfather, though, especially enjoying looking through photo albums and learning about the mother she couldn't remember. Patrick enrolled Terry in the Loreto Grammar School in Omagh, County Tyrone when she turned 11. The school was about a 40 minute drive from their home in Enniskillen, which gave her and her grandfather a bit more bonding time, as he insisted on driving her to and from school himself each day. The private, Catholic school was the best in the area, scoring high across the board for academics, and Patrick wanted her to get the best possible education she could. Attending an all-girl school wound up giving Terry a chance to really come into her own. She gained confidence in herself, made solid friendships, and excelled in her classes.


When Terry was 14, Sean returned to Cassidy Keep unexpectedly after a mission gone wrong. He was injured, but refused to let anyone help him. Given his regular absences during her time at the Keep, Terry still hadn't developed much of a relationship with him, which ultimately led to an argument. She didn't feel she could trust him, and he didn't believe she was making the right decisions while not in school. The argument quickly escalated, only to end abruptly when Terry opened her mouth and a scream came out instead of the words she'd intended.

Luckily, Sean was more than proficient with his own powers and managed to shield himself from the sonic blast Terry had unintentionally unleashed. The blast ricocheted off of Sean's sonic shield and left a sizable impact crater in the ancient keep's stone wall. Needless to say, Terry was horrified of what she'd done. In tears, she ran away from Sean, holing up in her room and refusing to open the door, no matter who knocked or what they said. A full two days passed before Sean used his abilities to unlock the door and get into her room.

He brought food, which Terry appreciated even though she refused to admit it, and they had a tentative conversation about mutations. Terry was still in shock over what she'd nearly done, the pure violence of it, but Sean explained that he believed, based on what she'd done, that they had a similar powerset. He told her about using sonic vibrations to gently tweak the lock on her bedroom door, then demonstrated with the latch on her window so that she could see her abilities weren't inherently destructive — she just needed to learn control.

Sean offered to teach her.

That summer, Terry and Sean actually managed to work through some of their issues, bonding over their powers and the things that they could do with them. They enjoyed their time together, such as it was, but around the time Terry was set to return to Loreto Grammar School, Sean got a new assignment and left. His departure didn't completely ruin the progress he'd made with Terry, but it certainly set them back a ways.

The Underground

She'd managed to learn enough control to prevent any further incidents, at least, and when she accidentally shattered a tree while practicing on the Keep's grounds, her granda decided to seek out some additional assistance. Patrick revealed that he'd been a part of an organization meant to protect visible and potentially dangerous mutants for decades, ever since his brother-in-law was killed for having a visible mutation. The organization called itself the Underground and had been operating in various capacities since the Cold War. Though it was still bare bones in spots, Ireland's branch worked closely with the Muir Island Research Facility to place visible mutants in safe houses, enclaves, or solitary homes, depending on what the mutants wanted and/or needed.

These connections gave Patrick — and therefore Terry — access to a variety of people who could help with sorting out mutations safely when Sean was away. Terry became heavily involved with the Underground when she turned 16, no longer simply learning from those who actually took part in the organization's operations. She began actively helping to coordinate travel plans for mutants being relocated throughout Europe during the summer before she turned seventeen.

Sean wasn't entirely thrilled with her involvement in the semi-legal organization, but considering the good she was helping with — and feeling that he didn't actually have much of a right to attempt to direct her life or choices, since he was rarely at home and when he was they only really discussed powers training and development — he didn't attempt to stop her. Instead, when he could, he offered what information he had on international issues that might concern the Underground or help to prevent problems for their transportation/shipping routes.

Education & Career

After leaving Loreto Grammar School with top marks and an acceptance letter to Oxford University in her pocket, Terry prepared for furthering her education in the hopes of contributing more to the Underground and the world in general. She picked a Philosophy, Politics, and Economics BA because she felt it would give her the most advantageous starting point from which to plan the rest of her education and career.

She continued working with the Underground through her undergraduate and graduate studies, doing most of her active participation with them over holidays and breaks, focusing mostly on helping to map out travel routes and secure safe houses while at school.

After leaving Oxford with top marks and her Doctorate of Philosophy in International Relations, Terry managed to get a job right away. Médecins Sans Frontières hired her for an entry-level position in fundraising, which allowed her to get her foot one rung up on the career ladder. It's a ladder which she quickly climbed, using a combination of her education and a natural charm. Utilizing connections she made at Médecins Sans Frontières, she continued to work with the Underground.

In fact, thanks to friends from school and university, as well as those mutants she'd managed to place throughout Europe, Terry worked to bolster funding for the Underground specifically, always off to the side and anonymously.

It didn't take long for Terry to become one of the top fundraisers for Médecins Sans Frontières, a position which she enjoyed for a variety of reasons. It let her continue to network, which only benefited those she cared about and wanted to help, while also furthering a legitimately good cause. She was passionate about her job, often going above and beyond to help plan and execute parties, adding personal touches to make potential donors/guests feel welcome.

The Mansion

In the summer of 2018, shortly before her 32nd birthday, Terry wound up sitting down with her grandda and the Underground's UK organizer. The Irish and UK branches was well settled, but they all knew that several of their American chapters were suffering from an overflow of runaways and asylum seekers as their access to funding and safe houses deteriorated. The crackdown by local and state governments on mutants and those who supported them had begun to negatively impact their pipelines — those who'd long offered shelter to mutants on their way elsewhere, or financial assistance for things like clothing and food, began to back away from the Underground, afraid of what might happen to them and their families, should they be caught.

That fear of reprisal and legal consequences quickly began to stifle (and even destroy) the Underground in areas where it had once been successful. The Irish & UK Undergrounds' top coordinators agreed to divert what resources they could to their American counterparts, but they wanted someone specifically familiar with their methods to oversee the transfer of resources and to make sure they were being allocated appropriately.

They asked Terry to take on that job.

Because of the sensitive nature of the work she would be doing and the way the resources would need to be transferred, Terry needed to leave her position with Médecins Sans Frontières and take up a similar job in New York State. The decision was an easy one for Terry to make, though it left her feeling saddened. She did truly enjoy her work with Médecins Sans Frontières, and would miss the friends and colleagues she'd made there.

Luckily, a longtime associate of Terry's granda, Dr. Moira MacTaggart, recommended she look at an open position with the Xavier Institute. It became readily apparent that the Institute was an organization whose principles and tenants aligned with her own. With the job secured, she didn't hesitate to make her way to Westchester that fall — only to find upon her arrival at the location listed as the Institute's main address, that it was very much not what she had expected. Despite the surprise, she felt more than ready to tackle the challenges that would surely come her way.

Physical Characteristics

Height: 5'3"

Weight: 110lbs

Eyes: Hazel-green

Hair: Red


Non-Mutation Related Abilities

Talents of which a baseline human is capable with training and years of practice, but which Terry can manage with little to no effort. She just has a knack for them — a knack that's assisted by some of the physical adaptations caused by her mutation.

  • Circular Breathing: A technique used to produce a continuous tone without interruption. It's accomplished by breathing in through the nose while simultaneously pushing air out through the mouth using air stored in the cheeks.
  • Throat Singing/Overtone/Self-Harmonizing: This is accomplished by beginning with a droning note, then manipulating the lips, cheeks, tongue, and jaw to create two chambers in the mouth. With practice, it's possible to find the resonant frequencies of the chambers, then isolate and amplify the frequency of the note being droned to harmonize with yourself. The notes aren't being created, simply filtered from the drone note into smaller pieces.
  • Continuous Vocal Note: Terry can hold a single, continuous vocal note for three minutes (without utilizing circular breathing techniques). The baseline human world record for that is one minute and fifty-two seconds.

Physical Adaptations

Changes to a body wrought by its mutation that allow a person to utilize said mutation to its fullest.

  • Cartilage Elasticity: Rather than a baseline human's typical connective tissue (costal cartilage), which connects a human's first seven ribs to their sternum and vertebrae, Terry's ribs are attached front and back with elastic cartilage. This allows her lungs to expand much more than a baseline human's, which contributes to her ability to hold her breath.
  • Lung Capacity: The world record for a baseline human holding their breath is twenty-four minutes and three seconds. Terry can hold her breath for thirty-five minutes.


The ability to manipulate sound and sound waves. Sound is a periodic disturbance of the a medium: air, ground, water, etc. Sound radiates outward in straight lines in the form of a pressure wave. The effect these waves produce upon the ear is perceived as sound. From the point of view of physics, sound is considered to be the waves of vibratory motion themselves, whether or not they are heard by the human ear.

A person with Acoustikinesis can intensify, hush, and distort, as well warp, strengthen, echo, speed up, and slow down sound, using it as a powerful physical force and to propel themselves at high speeds. At low frequencies, sound is potentially fatal to living beings, given that it can cause internal damage. Since sound vibrations can travel through the air, ground, water and any form of medium, defense by using physical barriers is difficult. The vibrations can also affect people and objects at a molecular level.

  • Flight: Terry can use the vibrations of her sonic scream as a carrier wave for herself, allowing her to fly for as long as she's able to keep the sound going. She can scream for hours on end, so if she utilizes circular breathing techniques, she could theoretically fly for two or three hours at a time, but this would require extreme exertion on her part and she would need to take a break to rest. Flying for any length of time exceeding an hour is for emergencies only, as the break she'd need to take afterward would involve sleeping upon arrival, which means she'd be useless until she wakes up. She's not a speedster, so this would eventually take a toll on her physically, based purely on how she's best able to deal with outside effects like wind, temperature, etc, which further limits the distances and the conditions in which she can fly.
  • Sonic Scream/Lance/Resonance Frequencies: She can cause her vocal cords to vibrate over a wide range of sonic frequencies, producing a volume of sound ranging up to at least 140 decibels. Terry thus has the ability to shatter solid objects with her voice, should she reach the correct resonant frequency. Of course, she can also just use her sonic scream to blast through things, no resonant frequency required, but if she feels like being a bit more subtle than that, she's got the finesse to manage it.
1. The sheer force of her sonic scream is capable of killing people, if she lets it loose in an uncontrolled manner. It could break bones by itself, but there's every possibility that a person could collide with a solid object after getting the brunt of one of her screams. This could result in multitudes of injuries, including but not limited to crushed internal organs or severe whiplash.
2. By focusing her scream into a beam, typically using her hands to help her focus, Terry is able to create a sort of "battering ram" that can stun people as long as she keeps the vibrations wide enough. If she shortens them, however, she could break through solid objects in very small diameters. There's every possibility that, should she lose her focus while using her lancing ability, she could severely injure others or herself, so she's very particular about how and when she utilizes it.
3. Terry can shatter most common materials and objects (rock, wood, glass, ceramic, sheetrock, etc), but can't shatter solid sheets of metal or vibranium in any of its forms, since it outright absorbs vibration. However, if metal has been bolted shut or welded together, she can damage it at the seams enough for someone else to get in/out. She lacks the physical strength to bend metals herself, which would be the follow-up to her power for something like an escape.
  • Sonic Auditory Barrier: Terry can project a field of essentially noise cancelling soundwaves in a very localized area (a circle with a diameter of no more than twenty feet) — by listening to the sounds around her and then counteracting them with opposing waves that are of equal magnitude. This might cause people who pass through it to pause briefly, but since the barrier is meant to ultimately only keep sound in/out, there's no actual physical force produced. If any of the sounds she's canceling change, they are able to get through her barrier until she adjusts her own opposing soundwaves.
  • Sonic Shield: Terry can control the sound waves around herself and others within a ten to fifteen foot radius of her position, making a barrier against outside physical attacks — both ranged and melee. The shield is made of pure sound and does not seek to eliminate any frequencies. Terry has to expend an immense amount of energy/concentration to hold it up, since she's essentially manipulating the density of air by using the force of the sound she generates. She stops the soundwaves in front of herself -- or someone else -- and keeps the force of them, which would normally have blown someone/something away, from its natural dispersion. That, combined with the build-up of sound Terry continues to create, allows her to stop physical attacks -- for a time, at least. Magic can absolutely get through it, as long as the spell isn't attached to a physical object. If she's just keeping people away from herself/others, Terry can keep the shield up for around fifteen minutes before the strain starts to show. After that, she begins sweating/shaking and quickly has to sit down so she can focus purely on maintaining the shield. Holding it for longer than twenty minutes, Terry risks suffering a hemorrhagic stroke or a brain aneurysm.
She will often lose consciousness before damaging herself irreparably -- a natural/biological reaction to prevent her from killing herself -- which can last for a day or so. The shield is capable of stopping one or two bullets, but wouldn't be able to withstand a sustained barrage of gunfire for more than sixty seconds before shattering. Similarly, Terry can stop baseline humans from attacking her physically, but dealing with a superhuman battering against it, she's only able to hold the shield for around five minutes before it breaks. In any case, Terry would suffer physical symptoms of her shield snapping (or of maintaining it for long enough that she lost consciousness) -- a headache, a nose bleed, severe disorientation/confusion, and even unconsciousness would all be possible, depending on the length of time she'd been holding the shield. The longer the shield is up, the worse the effects will be for Terry when it breaks. In such cases, she would have to avoid using her powers for anywhere from a few days to a week or more -- it depends on the severity of the effects she suffered from overusing her powers.
  • Superhuman Vocal Stamina: Terry's vocal cords are tremendously strong, so she can produce sonic effects through screaming constantly for several hours at a time without noticeably tiring or injuring her vocal apparatus. Her vocal cords and the interior of her throat/mouth are also superhumanly tough, so that the intense pressure and constriction required for her to produce the effects she does don't cause her any injury. She is, however, susceptible to outside physical injury — if someone were to strangle her, for instance, she would suffer the same injuries as a baseline human who has been strangled (depending on how strong/violent the person strangling her is, this could result in long-lasting damage). She's also just as capable of contracting the flu, laryngitis, strep throat, the common cold, or dealing with allergies as a baseline human. That being said, while it would be painful, she would still be able to use her voice/scream for brute force defense/offense, if necessary. While ill, she wouldn't be able to use any of her powers that require more finesse than a simple scream.
  • Sonic Amplification: She can manipulate the sounds she makes or the ambient sounds around her, both increasing and decreasing their volume/intensity. Terry can also amplify sound carrier waves, allowing her to hear conversations or noises from up to half a mile radius around herself, and to pitch her voice so it's carried to people who are within that same radius.
  • Sound Immunity: Her hearing and equilibrium are unaffected by her mutation, no matter the way in which it's utilized, as well as the powers of others with similar abilities. She also possesses an immunity to her father's powers.
  • Vocal Disorientation/Unconsciousness/Death: The ability to change someone’s balance as long as they're within ten to fifteen feet of her, affecting their equilibrium through manipulation of the fluid in their inner ears with vibrations. This can result in dizziness, nausea, and ultimately unconsciousness. If the tone is maintained for long enough at a low enough frequency, Terry can cause significant internal damage. Ultimately, that could result in death.


Little snippets that reflect your character's personality.

External Links

xp_communication posts

xp_journal posts

xp_logs posts



The Danger Room Paradox


A Fistful of Nanites

Potomac Calls to Chesapeake

Monster Mash


Behold A Pale Horse


Player: Cai

Player Icon Base: Holland Roden

Meta Trivia

Cai picked up Terry as a P2 version in December 2018, using the traditionally female code name of Banshee. She played her until January 2020 when she became a Player Emeritus due to RL demands. She returned to pick up Terry again in March 2021.