Seisyun is a short young man, with long light blue hair tied back in a ponytail. He has a short and thick ahoge (single lock of hair sticking out from the top of the head) and large light blue eyes. He usually wears a blue robe and carries his Household Vessel, two small swords behind his back.
Seisyun is upbeat and usually seen with a smile on his face. He is shown to be protective and very loyal, especially to Hakuei. He gets quite annoyed when someone talks about his height, such as when Hakuryuu mentions how short he is.
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 stop him.
Some time later, Seisyun follows Hakuei to clear her suspicion of one of her soldiers being killed by an arrow. During their 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 feels 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 a 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 uses powerful Wind Magic from her Djinn, Paimon, 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 has. 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 ending of the fight 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 materializes Paimon. After that, Seisyun, as well as Hakuei and her army, bids farewell to Aladdin.
Seisyun is seen 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 to the funeral.
Seisyun is very skilled with dual swords.
- 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 Sougetsuken to unleash a gust of wind that is strong enough to knock back a group of soldiers.
Seisyun is very close to Hakuei and agrees with her ideals and goals. He is close to her to the point he is called an "old friend", a relationship that goes beyond that of servant and master. Having conquered a dungeon as well as having gone through many trials and tribulations together, the bond the two share is extremely deep.
Seisyun gets along well with Hakuryuu and does martial arts training together with him. But sometimes, the two of them were bickering about Seisyun's height and Hakuryuu being a crying baby. 
- His first name means Blue Hibiscus. His last name means Plum.
- "Seisyun" is the Japanese pronunciation; in Chinese his name would be Qīngshùn.
- Seisyun is annoyed that Hakuryuu grew taller than him.
- His special skill is dual-sword fencing.
- His hobby is reciting poems.
- His weakness is insects.