I Don't Care If I Become Evil, I Want to Kill You

Okiteru, an elementary school boy who lost his parents and lives with his unemployed older brother, spends his days performing intimate "services" for the adults who come through his brother's introduction.
One day, Okiteru, who spends his days in despair, becomes friends with a girl (boy) of the same age who calls herself Gabrielle, and receives a business card from her. Written on it was...

" A revenge business for children who are victimized by scum adults..." "We kill adults with certainty..." "Bad adults only."

It was a revenge business that punishes bad adults who prey on children——!?
It's a shocking violent suspense that questions "adults" and "children" and what "justice" is!!!!!!