Mutsuki is a mischievous prankster at heart, she often exposes Aru's true colors for fun. She even playfully teases and pranks Sensei, often making them uncomfortable. She's an 2nd year student at Gehenna Academy, Mutsuki holds the title of "Chief of staff" and is the assault activist and go-getter of Problem Solver 68 club. She is a trouble maker that likes bomb. She usually carries a black bag filled with bombs. But not this time. Aru is her best friend. Mutsuki knows Aru very well.