[From Essence of Purity]:

Makise Ryo, the student president of a catholic school, seems to be liked and admired by everybody, including his cute little brother even if the latter is somehow jealous of his older sibling. When Ryo gets abducted by delinquents from his school who wanted to "teach him a lesson";he's saved by a mysterious student. Gunta didn't help him out of sympathy but "just because they woke him up".

Later, Ryo meets him again & weird things start to happen...