The elder brother, Subaru, is very fond of his younger brother, Ryuusei. He has been raising his younger brother in a very sweet manner as a surrogate parent. Thanks to his efforts, he has grown into a lovable, angelic boy. Worried that he might catch a strange insect, he becomes a teacher at his brother's school and spends his days stalking him and fighting a solitary battle. Meanwhile, the younger brother falls in love with a student while under his watchful eye. When he finds out that his brother is in love with someone else, he decides to do everything in his power to destroy that love...

This is a funny school love comedy about an older brother who loves his younger brother too much and a naive younger brother.