pre, where did this happen? if this happened within the school premises, you could sue the school kasi they shouldnt have allowed an outsider inside the school. If you sue your school, the administration will then pressure your enemy to bring out his cousin. Pag di nila nilabas ang cousin nung kaaway mo sila ang mananagot. And dont allow that 2nd year student to get away with it. Dapat ma-expel siya on the grounds na he masterminded the beating. He is legally responsible for his action.
Now if you want to get even physically, you could wait for the bastard to be jailed and pay the inmates to beat the hell out of him. At least lamang ka na after that.