He is a short boy, with long light blue hair tied back in a ponytail. He has a short and thick ahoge. He usually wears a blue robe and carries his Household Vessel, two small swords.
Seisyun is shown as rather upbeat, and is usually seen with a smile on his face. He is also very loyal to Hakuei, standing by her side even as they faced an army.
Seisyun is seen accompanying Hakuei to peacefully talk with the Kouga Clan. However, Ryosai angers Dorji by hitting Toya, which leads to Ryosai wanting to retaliate, so Seisyun and Hakuei stops him.
Some time later, Seisyun follows Hakuei to clear her suspicion of one of her soldiers being killed by an arrow. During they're way there, they talk about Kouga not wanting the war. Hakuei mentions that Aladdin visited her the day before, surprising him. However, when Hakuei adds that she feel she can trust him, Seisyun smiles and says that if she does, he will as well. He also thinks that there must be a reason for meeting between Hakuei and Aladdin. Reaching the Kouga Village, Seisyun notices that there's no one there. In that very moment, the two of them are attacked.
Seisyun asks Kouga members to calm down, as they come here only to negotiate. He is terrified as he realizes that anger took care of them and wonders what Hakuei is going to do. She is attacked and slightly wounded, but all is somewhat cleared after Baba comes and declares that the Kouga will join the Kou Empire. Hakuei and Seisyun go back towards their base.
After that, Ryosai betrays them and orders their former army to attack them. Hakuei first blows away the arrows and when the army rushed in, Seisyun uses his Household Vessel, Sougetsuken, to buy Hakuei some time. She then Djinn Weapon Equips, however, she quickly, as well as Seisyun, runs out of Magoi. Hakuei orders Seisyun to capture Ryosai, who laughs at her and shows her how many people he still have. His army shoots her and Seisyun with arrows and quickly captures them. Seisyun is unable to continue the fight, but eventually Aladdin comes in and saves them.
Hakuei then goes to Seisyun's side and waits until he wakes up. Still being barely able to talk, he asks Hakuei about her state and about the punishment Ryosai got. She tell him about the fight's ending and Aladdin's identity as a Magi, which surprises him. Hakuei then introduces Seisyun to Aladdin, with Seisyun still being quite surprised, so he stays silent. He is stunned when Aladdin summons Paimon. After that, Seisyun, as well as Hakuei and her army, bids farewell to Aladdin.
Seisyun is rushing to the Kou Empire on a horse along Hakuei Ren, who will attend the Emperor's funeral, and the members of the Kouga Clan. A day after arriving, he follows Hakuei at the funeral.
- Seisyun is very skilled with dual swords.
- Seisyun uses the powers of Hakuei Ren's Djinn, Paimon. Paimon lends her power to his Household Vessel, Sougetsuken.
Sougetsuken (Double Moon Swords)
- Using Paimon's wind, Seisyun improves the slashing power and range of his swords. However, if Ren Hakuei runs out of Magoi, he cannot use this ability.
In the anime, Seisyun has also used Sougestuken to unleash a gust of wind that is strong enough to knock back a group of soldiers.
Seisyun gets along well with Hakuryuu and does martial arts training together with him.
Seisyun is very close to Hakuei and agrees with her ideals and goals. It is unknown how these two meet, but they seem to have complete trust and faith in each other. He helped her capture Paimon's dungeon.
- Seisyun is annoyed that Hakuryuu grew taller than him.
- He likes reciting poems and his weakness is insects. His special skill is dual sword fencing.