When Rui was little, he and his best friend, Tsukasa, got kidnapped by some strange men and were used as lab experiments. Tsukasa got turned into some demonic being while Rui was just given octopus tenticals, platypus venom, cat ears and tail, and his tenticals can sting like a jellyfish. Currently, Rui was being dragged to Tsukasa’s cage since the scientists couldn’t calm him down by feeding him other human experiments, so whenever this happens they put Rui in the cage to calm Tsukasa down.