"What did you do? What did you do?"
After a powers mishap brought on by borrowing Kurt's mutation before prom, Marius's condition began to steadily deteriorate. Frustrated, and fearing that the school cannot help him, he abandons the school, leaving behind notes for his friends and most of his possessions. In a fit of self-preservation Marius takes the trouble of arranging travel to Spain, where his friend and former classmate Manuel has agreed to provide him with marrow while he searches for some kind of grasp on his situation.
In one of the events of questionable chance that compose Jennie's life, a month later a Paris layover from visiting her family in Italy ran Jennie right into the stranded Marius and Manuel. The next day both the school and Jennie's father received conflicting phonecalls about her whereabouts. Jennie subsequently disappeared.
Eventually, the alarm was raised and the staff began following what was a very cold trail. X-Force was called in to help, as the group specialised in investigation, and eventually, they caught a break - Doug Ramsey and Marie-Ange Colbert, working through security footage of various casinos, identified the two runaways in the company of Manuel. Alarmed by the implications, the X-Men sent a team to France, where they met up with Wanda Maximoff who had been investigating contacts in France with Remy LeBeau. The missing students were tracked to a hotel, where Ororo Munroe and Kurt Wagner made a horrifying discovery - a comatose young girl with razor-sharp dark red skin, who had been obviously fed upon by Marius. He had bought her from a mutant slave ring in Paris, and used his power to change his own cells from the maladaptive form they'd taken. Her name, he'd been told by the slavers, was Penance.
Jennie, Marius and Manuel were found at a local nightclub, but on seeing the teachers, unaccountably panicked and fled. Jennie and Manuel, using her powers to escape pursuit by Wanda and Rahne Sinclair, found themselves on the wrong end of a lucksnap caused by over-use of Jennie's good luck. Jennie was almost hit by a runaway truck, and it was Manuel who saved her life by pushing her out of the way and being hit himself. Marius then arrived to see his two friends unconscious and injured, and snapped, attacking the arriving X-Men. It was only Kurt beating him senseless with a brick that brought the scene to a violent end.
Eventually, back at the mansion, it was uncovered that Marius, feeding on Manuel, had inadvertently created an empathic loop that had trapped all three of them. The loop was removed by Charles Xavier, but the damage to the friendship between Jennie and Marius had been done. Penance - later identified as an Albanian girl by the name of Yvette Petrovic - was brought back to the school for assistance and Manuel was relocated to Muir Island Research Facility, where he remains in a coma.