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.

As Mahiro stumbles through his new life as a girl, he finds himself gradually beginning to get into the swing of things. Realizing this, however, prompts him to try and reclaim some of his masculinity. He tries, in futility, to engage his core and do a sit-up, but ends up with a stomachache instead. Seeing his condition worsen rapidly before her eyes, Mihari has an epiphany. She realizes that his pain may actually have something to do with fact that almost a month has passed since Mahiro turned into a girl...

Mahiro loses to Mihari in a video game, so he has to do the grocery shopping this week as punishment. As an unemployed, good-for-nothing shut-in, the task at hand is daunting, but he plucks up the courage and makes his way towards the supermarket. The size of the crowd, however, makes his resolve waver and Mahiro finds himself cowering outside the store entrance. It is then that a young boy (?) around his age, wearing a baseball cap, comes to the rescue and offers him a helping hand. Thanks to the boy's (?) help, Mahiro is able to buy the groceries he needs and is just about to head home, when Kaede suddenly shows up. Seemingly, out of nowhere.

Momiji shows up at Mahiro's house with her two classmates, Asahi Ohka and Miyo Murosaki, to invite him out for parfaits.

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.