Kotaro Uchikoshi

With his last memory being that of his kidnapping, college student Sigma awakens to find himself trapped in a facility with eight strangers. The captives are soon informed that if they want to escape, they must play the "Nonary Game"—a complex contest of trust and betrayal, where deciding whom to believe in is the difference between life and death. To make matters worse, any initial trust between the players is tainted when they realize that the mastermind behind their predicament may be one of them...

High schooler Yūta Iridatsu has experienced “astral projection” i.e. his spirit has been separated from his body. He woke up in a mansion named Koraikan and met a cat spirit named Chiranosuke, who told him “You must find the Sacred Tome of Koraikan in order to return to your physical body.” While searching through corridors of Koraikan, Yūta bumped into underpants of its female residents, and doing so would, eh, create some big trouble for planet Earth.