Nothing is more important to Seiichirou than his family. He protects the earth in order to keep them safe from harm. Seiichirou's father died when he was young so, besides Daisuke, they are his only family. He is able to be strong because he desires to protect them no matter what. Not only does their presence keep him physically strong, but they also keep him emotionally stable as well.

Shimako is his beloved wife. They met when they were both students in college. Even though he spent many nights awake studying, he still found time to spend time with his girl friend. While they were dating, she told him that her happiness was her own responsibility and she wanted to be with him more than anything. In a sense, she was the one who proposed to him. They spent their honeymoon in Atami and he promised that they would go there for their 10-year anniversary, which he hopes they will be able to do once the fate of the world is decided.

Yuka, his precious daughter, is in her first year of kindergarten. Seiichirou hates to be away from her because she is afraid of ghosts, just like her mother is afraid of cockroaches. She likes her cousin Daisuke, but her father teases her saying that she is too young to marry. She most likely knows nothing of her father's duty, since such knowledge would only scare her. She clearly adores her father and he loves her more than anything in the world.

One time he and Daisuke were discussing the end of the world and Seiichirou's role as a Seal. In the midst of a very serious conversation, he gets excited when he sees a soda machine with a drink his wife loves. He buys her and Daisuke one, but his nephew cannot understand why he is so exited about a drink when they were discussing a very serious topic. Seiichirou explains that he cares more about the drink than any philosophical or spiritual issue. If he can make his wife happy by finding her something she likes, that is the most important thing in the world. Daisuke seems to understand that.

Seiichirou has promised his family to always come home safe and happy. In turn, they made the same promise to him. With the end of the world drawing near, it may be a difficult promise to keep, but hopefully he will survive to return home to his family who love him dearly.