Matsuri Kazamaki is a ninja exorcist sworn to protect people from ayakashi, the malevolent spirits that prey on humans, and above all to guard his childhood friend Suzu Kanade, a medium whose strong spiritual power draws them to her. When the powerful cat ayakashi Shirogane sets out to break the pair apart, he casts a forbidden spell that leaves Matsuri trapped in a girl's body. Matsuri has to keep shielding Suzu from spirits while living in a form that complicates the feelings already between them.