Family
Above all else, Seiichirou's wife Shimako and daughter Yuka are the most important part of his life. They are the reason he can create a kekkai, the people he wishes to protect. In his side story in volume 12, he explains to a much younger Daisuke that in order to become stronger, one needs to have someone or something that he or she wishes to protect. For Seiichirou, those people are Shimako and Yuka. They not only strengthen Seiichirou's power, but his resolve to fight for the human race as well.

Much of what we know about Shimako and Yuka comes from Seiichirou's character file, which is in the form of an e-mail he is sending to them. Yuka is in her first year of kindergarden (there are two such years in Japan), loves her cousin Saiki, and is afraid of ghosts. Seiichirou and Shimako met in college and have been married for nine years. Their tenth anniversary is coming up, and he plans on taking her to Atami (where they went for their honeymoon). Shimako also happens to be afraid of cockroaches and loves pudding juice. And apparently, she was the one who proposed to Seiichirou. How cute. ^^

Sometime around the middle of the TV series, Seiichirou attempts to file for a divorce (he's is hindered by the discovery that his friendly neighborhod ward office employee is one of the Chi no Ryuu). His reasoning is to keep Shimako and Yuka out of danger, though he planned to re-marry her after the Final Battle. That's quite the Seiichirou thing to do, but maybe not one of his better plans of action. Her presence in his life, as well as Yuka's, are necessary to keep his resolution strong. They are a microcosm for his world: Seiichirou wants to protect his daughter and wife, and thus he protects the earth.

Neither Shimako or Yuka appear in the manga. The only time their faces are shown is in episode 21 of the TV series, when Seiichirou pockets a picture of them on his desk before his second confrontation with Yuuto. Shimako is an attractive woman with short black hair, while Yuka an energetic, wide-eyed and crowned with two short, brown pigtails.

Hajime - Uchi