A 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. Contrary to her guilt-riddled childhood friend Aru, she is a devilish troublemaker and commits acts of wanton wrongdoing without hesitation. No one can read Aru better than Mutsuki, so she understands her friend's bluff better than anyone else, even if she doesn't give any particular thought to the matter.