Kaoru's Grandfather. Kaoru's scars on the back was due to Gen'ichiro hitting him violently with bamboo cane when Kaoru has been trying to protect the mementos of his dead mother.

Manga only:
When Kaoru came back to Hanabishi for a probabilty to become it's heir again, he found his grandfather to be sick and weak old man. Gen'ichiro didn't even recognise Kaoru as his grandchild, mostly because of the Kaoru's brother who pretended to be Kaoru.
Manga only part2:
Gen'ichiro's dying will was that Hanabishi clan be inherited by the man who marry Aoi. Kaoru's brother been keeping it secret for his own advantage.