Isaku

"The day came when the hideous fiend was gone, forever."

- Kotomi upon relief of seeing Isaku dead

Isaku is the main antagonist of the OVA Isaku Respect. He was the janitor at the school the protagonists attended, and it is clear from the start that he is not only a pervert, but a pedophile as well. Somehow, he acquired blackmail on all of the girls and used that to lure them to the school while it was empty. He captured them one by one and forced them to be his sex slaves. He would frequently slap the girls for insubordination. He had never said a single word through the series.

After a long night of endless torture by his hand, the girls awaken to find Isaku lying on top of Kotomi, dying with a big smile on his face. He was never formally prosecuted for his crimes as he was dead, but after some time, the girls begin to move on from the scars Isaku left on them.