Masaki Umeo is a middle schooler with a nasty temper. Because of his temper, he is causing all sorts of problems and is constantly involved in fights causing his sister to worry about his well-being. One day, he stumbles upon an Aikido class which he becomes interested in, but soon dismisses it until he meets Daniel- an english teacher from Canada.
He wants to become much stronger in order to defeat his older brother, Shigeru, which had been very violent with his mother. Eventually, he (Shigeru) ended up being stabbed by his mother. Shigeru return one night home and fights with Umeo, and also explains to him that he will eventually become like him and his father, because violence is in their genes.
(Source: Hidoi~! Translators)