Ok - the guy's being bullied endlessly at school because of his facial birthmark. In the first scene after he attempts suicide, he wakes up and find out that his sister's committed suicide in the tub instead.
At school, we see a daily life of the guy being bullied - normally his sister would protect him while the girls who bully him also take advantage of her (To extort money from her amongst other things). In school, the guy learns his sister survived but is in a vegetative state.
However at the end of the day, the guy vows to take revenge on the bullies after he receives news that his sister passed away. After the rooftop rape scene, somehow his (magical??) iPad is able to channel her spirit/his rage/some revenge power into him, turning him into his sister (which freaks the leader of the bullies the F out).
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