Ren Mihashi was the ace of his middle school's baseball team, but due to his poor pitching, they could never win. Constant losses eventually lead to his teammates bullying him and reached the point where his teammates no longer tried to win, causing Mihashi to graduate with little self-esteem. As a result, Mihashi decides to go to a high school in a different prefecture where he has no intention of playing baseball. Unfortunately, upon his arrival at Nishiura High, he is dragged into joining their new team as the starting pitcher. Although unwilling at first, Mihashi realizes that this is a place where he will be accepted for who he is; with help from the catcher Takaya Abe, he starts to have more confidence in his own abilities. Abe, seeing the potential in Mihashi, makes it a goal to help him become a pitcher worthy of being called an ace.

Self-professed home security guard Mahiro Oyama has not left his home in years, secluding himself in his room playing erotic visual novels. This depraved lifestyle causes his prodigious sister, Mihari, to worry about his well-being. In hopes of solving this problem, she devises a plan to rehabilitate him back to normalcy. The first part of Mihari's plan is to concoct a medicine that changes her brother's biological constitution into a bona fide female, much to Mahiro's vehement dismay. Stuck in this predicament, Mahiro has no choice but to live out his life as a cute girl until the effect wears off—if it ever does.

Kirino Kousaka embodies the ideal student with equally entrancing looks. Her grades are near perfect, and to cover her personal expenses, she works as a professional model alongside her best friend Ayase Aragaki, who abhors liars and all things otaku. But what Ayase doesn't know is that Kirino harbors a deep, entrenched secret that will soon be brought to light. At home one day, Kyousuke, Kirino's perfectly average brother, stumbles upon an erotic game that belongs to none other than his seemingly flawless little sister. With her reputation at stake, Kirino places a gag order on her sibling while simultaneously introducing him to the world of eroge and anime. Through Kirino, Kyousuke encounters the gothic lolita Ruri Gokou and the bespectacled otaku Saori Makishima, thus jump-starting an entirely new lifestyle. But as he becomes more and more involved in his little sister's secret life, it becomes that much harder to keep under wraps.

After receiving a flyer from Maina Ichii—a member of the idol group ChamJam—and seeing her perform at a local concert, Eripiyo falls in love with Maina and decides to devote her life to supporting the shy and reserved rising star. Eripiyo's charismatic presence and iconic red tracksuit soon give her recognition as Maina's one and only unrivaled fan. Whether it be a performance or a small fan gathering in the middle of nowhere, Eripiyo is guaranteed to be at every event Maina participates in. Not even an injury or Maina's seemingly cold attitude toward her can stop Eripiyo from pursuing her dream of seeing her beloved idol perform at the world-famous arena Budoukan.