There's only one thing that gets a certain 16-year-old boy to wake up early on a Sunday morning—the weekly broadcast of his favorite show, Magical Girl Pretty Eririn (PreEri)! But as much as he loves magical girl anime, Rio Aoi feels too ashamed to let his interest in a children's show be known to the public. In order to have as little contact with his classmates as possible, he usually leaves school immediately after classes, excluding some occasional shopping for PreEri merch on the side. This is how he currently spends his high school days.

However, this routine is suddenly broken when Aoi saves a girl falling from the sky who was trying to fight a monster. The next day, she finds him at school and introduces herself as Nagi Sumire. Despite being a magical girl, she is not sure what she should do and has yet to defeat a single enemy. While trying to boost her confidence, Aoi accidentally lets his knowledge of PreEri slip. But to his surprise, Sumire reacts excitedly and quickly asks him to teach her about magical girls!

And just like that, a supportive friendship—along with some extensive training—begins.