Ninja trainee Shinobu goes on a mission by her perverted headmaster to collect underwear from high school girls, first targeting Kaede Shiranui.

Rainy weather drives bored ninjas into looking for the Loch Ness Monster in their pond, only to find an Onsokumaru-eating crocodile instead; girl-girl dating.

Onsokumaru gets angry at Shinobu's little sister, Miyabi and decides it's time for a little one-on-one; Shinobu is kicked out of the manor, and heads to Kaede's family.

Rising temperatures provide a perfect opportunity for Onsokumaru to get Shinobu and Kaede into their swimsuits and, possibly, something more intimate.

Onsokumaru is sent to Hell and encounters demon schoolgirls, demon wives, and demon in-laws; when it's too hot to train, the ninjas plan a Summer Festival to brighten the mood.

With Shinobu stuck at Kaede's house under threat of a typhoon, those left at the ninja manor witness Onsokumaru's darkest hour.