Whilst Akane's class goes on a summer school field trip to Shikine Island, they are requested by Mizuha to turn in their Operation Keys for the duration of the trip. Unbeknownst to the girls, this is part of an experiment by Kenjirou to increase their 'friendship power'. To this end, he 'kidnaps' Rei and puts on a phony Alone alert, leading the girls towards an obstacle course of his design, filled with all sorts of traps. Not considered in his plan, however, was Rei escaping from her custody and assisting the girls in a not-so-subtle disguise...