https://projectsekai.fandom.com/wiki/Kamishiro_Rui

Kamishiro Rui is a 2nd-year student at Kamiyama High School. He is a member of the musical show unit Wonderlands x Showtime.

Rui lives by his own set of rules, which causes people to consider him a weirdo. He’s almost always smiling & sometimes gets carried away by his eccentric ideas. This includes using people as test dummies for his ideas & waterboarding them in swimming pools. Despite the riskiness of his ideas, he still considers safety.