After being fired from his company due to his violent temperament, Takehisa returns to his family home for the first time in 7 years. He finds that his previously angelic little brother, Rio, who used to adore him, has grown into a handsome and intelligent but devious person. While somewhat contemptuous towards his older brother, the two manage to coexist for the most part. That is until Takehisa sees his brother having a sexual encounter with a random man in a park restroom...

(Source: KOOI., translated)

Note: Includes an extra chapter.