From xkazemg:

Tomomi left Hokkaido to stay with her relatives, the Sendouji family, during the course of her university study in Tokyo. The Sendouji is renowned locally for its karate dojo that is instructed by the four brothers.

Tomomi remembered spending her childhood times playing together with the brothers when they were little. As she met up with the brother again, things were quite different to how she had imagined it to be. For instance, Soryu, the third brother, was forever cold towards her, whilst Kouryu, the second brother, always teased her and looked down on her.

Luckily for her, she managed to find comfort in Hakuryu, the youngest and most gentle brother who had just returned to the family after being away for a long time. But to everyone’s surprise, Hakuryu returned home with a toddler son with no wife. Increasingly, Tomomi found herself being attracted to Hakuryu, but he was heart-broken after finding out about his wife, who died giving birth to their son and whom he still dearly loved.

Meanwhile, Tomomi started practicing karate with the brothers in their dojo... She began to find interest and passion for martial arts, which later brought her to national Fighting Championships!