Takatou Iori, a high school student, while on his way to confess to the girl of his dreams, just so happens to see a little girl who is about to get hit by a car. In an act of heroism, Iori jumps in to save her, and gets critically injured. Thankfully, he is saved by the super genius, Kusanagi Yume. Unfortunately, Yume is a female lolicon, and has turned him into a loli!
Now a elementary school girl, Iori has to live under the same roof as his crush; Kusanagi Mikuru, who just so happens to be the younger sister to Yume. All that, coupled with the fact that he has to start going to the same school as the little girl he saved, Iori has got his worked cut out for him.