On his way to school, Torii Akira helps a girl who was about to fall down. From that moment he keeps running into that girl, and she seems very happy to see Akira. Could this be the reason Akira can't help but smile all day?

Before long, however, Akira begins to notice the true face of that girl. Her obsession growing every day, Koharu's eccentricity causes her to take anything involving Akira to the extreme, disregarding the concerns and well-being of others as she seeks her senpai's affection.