Y/n is one of the strongest x-man, s/he's a vampire, has to eat organs and drink blood to survive, but s/he's with the x-men, everyone trusts her/him. One day a student hits her/him with his power not on purpose, the power of the student makes the person he touches go back (with the mind) when the person had the half of the actual ages (example: a person is 50yrs old and with that power the mind of the person goes to the past when he was 25 years old even if the body is still the same). Y/n is really old, and s/he became "good" only since 10 years, s/he's also very old, s/he's probably about 1000 years old, her/his mind will be of when s/he was 500 years old for an entire day...