|Series||Tsubasa: Reservoir Chronicle|
Make virtual worlds/dreams reality (through Sakura's feather)
|Tsubasa: Reservoir Chronicle Chapitre 37|
|Tsubasa Chronicle Episode 18|
|Tsubasa: Reservoir Chronicle Chapitre 232|
|Tsubasa Shunraiki Episode 2|
He appears as a mysterious traveler from Syaoran's past who also gained the power to travel between worlds from Yūko Ichihara, the Dimension Witch. He is currently searching for the vampire twins, Kamui and Subaru, and, like his younger brother, he is a treasure hunter, not a vampire hunter like originally believed. His abilities include summoning Oni to fight for him. He is able to perform these abilities with the help one of Sakura's feathers, which Syaoran failed to retrieve in their encounter in Ōto Country. An experienced fighter, Seishirō was also the one to teach Syaoran how to fight by utilizing the longer reach of his legs to compensate for the lack of sight in one eye.
Seishirō has black hair with seemingly no part and gray eyes. He is normally seen wearing a black shirt with a white lining that goes all the way up his neck and a hooded tan cloak. During his time in the Clow Country, he is seen wearing a black shirt, white scarf, and a tan robe.
Even in battle, Seishirō keeps a calm and collected air around him. He will not stop until he find the "I" level Oni that he has been searching for. Even though he had a bond with Syaoran, he was still willing to attack him.
Syaoran was holding a book that his father had been searching for years, when several villagers corner him and demand that he hand it over to them. He refuses and one of them begins a punch, only to be stopped by Seishirō. Effortlessly, he hits and throws the men before they are all on the ground. He then turns to Syaoran, who thanks him. He says thanks aren't necessary, and that he wants the book as well. Syaoran puts up his guard, but Seishirō tells him he only wants to look through the information about the vampires he had been searching for. Trusting him, Syaoran gives him the book.
Seishirō warns him that he could just be a thief, but Syaoran gives it to him anyway. They are later seen going over the book and Seishirō comments that he cannot read the ancient language of Clow. Syaoran notices that Seishirō's eye is false, and he responds by saying Syaoran is the same. Syaoran agrees to read the book to Seishirō, in exchange for Seishirō teaching him how to fight.
Seishirō first appears as a shadowy figure in the town, watching as an oni attacks regular townspeople. Later, as Fay asks a young singer about the occurrence, we see him conjuring the oni while standing on a large clock face. He laments on the fact that the oni are getting harder to control and reveals Sakura's feather. Syaoran and another oni hunter rush into battle once they realize the oni have surfaced. There, Syaoran notices Seishirō up in the sky and remembers him from the past. This leaves him stunned, especially when Seishirō calls out his name.
Later, as Syaoran and Kurogane look into the incident, Seishirō confronts Fay in the cafe. He asks if the oni hunters are there, to which Fay responds no. Surprised that Fay is not a hunter, yet has such magical energy, Seishirō summons several oni. Fay leaves protecting Sakura to Mokona, and speculates that Seishirō's power to travel dimensions is actually Sakura's feather and that the Dimensional Witch gave it to him. Seishirō agrees and says his payment was his right eye. He then attacks Fay and he dodges. Seishirō comments that it would be easier if he was to use his magical abilities, but Fay says he has stopped using them. A bright light engulfs the room and both of them are gone.
Syaoran finds Seishirō and sees Sakura's feather. He asks where Fay is, and Seishirō tells him that he has died. Seishirō froms the two oni hovering around him into a weapon and stabs Syaoran, just as Sakura approaches. His body begins to disappear, as does Sakura's when she hugs him to say goodbye.
Later he appeared in Nihon Country and discovered that Fay had vampire blood. Initially he thought Fay and his friends knew the location of Subaru. After realizing they didn't, he intended to leave Nihon, but was challenged by Syaoran for the feather. Seishirō remarks how Syaoran is like his father, referring to Syaoran's true father and not Fujitaka, the adoptive father of Syaoran's clone throughout the battle. In Tsubasa Chapitre 189, it was revealed that Syaoran Li was Syaoran's father. How Seishirō knows Syaoran has not yet been explained.
After Syaoran unleashed his ultimate spell (all four of his elemental spells combined) on Seishirō, he reclaimed the feather and was sent into the Dream alone to rescue Sakura's soul. However, it seems that Seishirō intended to give the feather to Syaoran; his brother, Fūma, remarks, "You were planning to hand over that feather right from the start, weren't you? To that kid [Syaoran]."
Although Seishirō is not seen in the main story again, at the end of the manga, Seishirō can be seen in an unknown world, having apparently found Kamui and Subaru along with meeting up with his brother again..
Powers and Abilities
Hand-to-Hand Combat: As seen when protecting Syaoran, he is an agile fighter. He effortlessly pummeled the thugs, and was the one who taught Syaoran the ways of unarmed combat.
Oni: Seishirō has the unique ability to control oni. This power is limited, though, and he states it is hard to control higher level oni and that making them attack humans are difficult. He was also able to form several of them into a large sword-like weapon.
Inter-Dimensional Travel: Using the feather given to him by the Dimensional Witch, Seishirō can travel through dimensions. However, as stated by Fay, the number of worlds he can visit is limited.
Shikigami: Similar to his Tokyo Babylon / X counterpart, Seishirō can summon a black hawk-shaped shikigami which he can use as a sword. This weapon is unique since its shape and consistense cry during the battle
Vampiric Characteristics: Due to having drunk Subaru's blood, Seishirō is implied to have vapiric powers, such as an extended life spam, regenaration and enlongment of claws, though he hadn't demonstrated totally this abilities as of yet.
- Despite not being his signature as it was in his original series, Cherry Blossom Trees have been present in every fight in which Seishirō has taken part onscreen (except in Clow Country's flashback).
- Like his original did with Subaru, Seishirō was impressed with Syaoran's pure and innocent heart when they first met.
- Seishirō appears in Chapitre 6.1 of Tsubasa World Chronicle: Nirai Kanai-hen, where he is the priest of a world that Syaoran and the group visit. It is not made clear whether this is the same Seishirō or that world's version.