Many of the characters in X are extraordinary people living extraordinary lives. Aoki Seiichirou lives a very normal life as a husband, father, and editor despite being directly involved in the end of the world. In the midst of an epic battle for the future of the human race, Seiichirou remains surprisingly normal.

Seiichirou is very kind and cheerful. He is as optimistic as anybody can be when he or she is involved in the end of the world. Considering the cynicism about humans inherent in X's narrative, he believes in the goodness of people despite their flaws. A people person, Seiichirou seems to put people at ease even under trying circumstances. Perhaps one of the most remarkable things about Seiichirou is his sense of chivalry. He treats woman with respect and consideration, yet he manages to avoid appearing condescending. His sensitivity towards people is completely effortless because he is not trying to convince anyone. He simply does what he thinks is right and is probably surprised that others do not do the same.

Seiichirou's appearance highlights his normality. His features are handsome but mature, unlike his younger comrades who are cute in their adolescence. His brown hair is stylish but professional and gives him a lighter appearance than more angsty, black-haired Dragons on both sides. Glasses cover his adorable, brown eyes. He smiles a lot which makes others feel comfortable in his presence. Usually he wears professional, brown suits which accent his broad shoulders and brown hair. On occasion he wears slightly more casual outfits-usually jeans with a belt and a nice shirt. Whatever he wears, he looks nice and neat.

He works as an editor at Asuka Magazine (which is the publication X use to run in). His job requires many hours spent in front of a computer, though he does go out and research topics for his writers. He met Karen during such a research session when he interviewed her at her bathhouse for one of his writers. He seems to enjoy his job even though it keeps him quite busy. It is a normal job with fairly regular hours, which allows him to go home to his precious family.

His family consists of his wife and daughter, and he would do anything for them. He constantly talks about them with great affection. They make him happier than anything else on earth. His desire to protect them gives him the strength to create a kekkai (or spirit shield) which protects the real world from being damaged when one is engaged in battle. In addition, he has a nephew named Daisuke who shares his power as a windmaster. Daisuke is dedicated to the dreamseer Hinoto and has sworn to protect her with his life.

In spite of his common job and family situation, he is a windmaster-the most powerful in his family. He controls the wind and can form sharp currents that cut and tear, but he can also use the currents to protect. Although no where near as powerful as Kamui (can be), Seiichirou has proved himself to be very valuable in battle. Another power he possess is the ability to create a kekkai-an ability belonging exclusively to the Ten no Ryuu (Dragons of Heaven). He is one of the chosen seven who fight to protect the world from destruction on the Promised Day. Not only must he use his power to protect the earth, but he also protects Kamui-the boy chosen to decide the fate of the world.

Seiichirou is the primary father figure in the story. He is balanced, confidant, and moral-he possesses a stability the younger dragons lack. He brings both optimism and maturity to the Dragons of Heaven ensemble.