We follow Mahiro Oyama, an unemployed good-for-nothing shut-in, who not only hasn't left the house in two years, but is also exceedingly addicted to gross video games. One afternoon, he wakes up and notices that his body feels a little off. Finding that strange, he goes to reach for his tablet, but what does he see in his reflection, but an adorable young lady. I wonder what lies in store for the "former" big brother, Mahiro as he's thrust headfirst into his new life as a girl.

Mahiro and the girls take a trip to a Japanese inn over spring break. First they hit the town in their yukata, before heading to the open-air bath to detox. However, things go south when Mahiro begins to feel a familar tingling sensation between his legs.