Луи Сент Крокус

"Rui" is a person who has been given the mysterious drug created by the yakuza group Garyukai, increasing his reflexes, agility, and speed to superhuman levels. He is ruthless when it comes to killing people but will turn into a quivering mess when shouted at by Tsukasa. When snapped out of the influence of the drug, Rui has a quiet and timid personality. Having grown up without a mother, Rui attached himself to his father instead, and accompanied him on numerous botanical expeditions. During one expedition to India, the two stumbled upon the kagi and a map that pointed out the location of the plant that would eventually be used to make the drug. His father presented the discovery to an academic board that happened to contain a member of Garyukai, which led to the secret falling into their hands. Rui is the one who severs Asago's right arm, under the influence of the drug. Note: the translation incorrectly refers to Rui as female a few times.