The Darkside Society Organization ("DSO"), oftentimes referred to as "Reverse Society", is a mysterious organization which acts as the true villain of the Rival Schools series.
Very little is known of this organization, other than their ultimate goal is to take over Japan and eventually the whole world. They have various clans of assassins working for them, among them the Imawano clan.
- Mugen Imawano: Apparently one of DSO's head members and the father of both Kyosuke and Hyo, he have died for reasons undisclosed and his evil spirit was sealed within Hyo's sword.
- Raizo Imawano: The brother of Mugen and father of Batsu, he defected from the organization for disagreeing with their ideals and founded the Justice High School. Was brainwashed by Hyo in the first game, which kickstarts the game's plot.
- Hyo Imawano: Son of Mugen and twin brother of Kyosuke, he's been brainwashed by his father since a child as to further the organization's goals. Acts as the main villain in the first game.
- Kurow Kirishima: An assassin working for DSO, who is sent to dispose of all Imawano clan members after Hyo fails. However, he has his own agenda, seeking to rule Japan all by himself.