He appears as a kind veterinarian who shows romantic affection for the young exorcist (referred as onmyōji) Subaru Sumeragi.

Since his introduction in Tokyo Babylon, publications for manga and anime have received Seishiro favorably for his relationship with Subaru, which became one of the most famous rivalries in X.

His role in Tsubasa: Reservoir Chronicle also received positive responses for his action scenes and connections with the protagonist Syaoran.

Seishiro, with twin characters Subaru and Hokuto, were created by series creator Nanase Ohkawa for a dōjinshi novel about an onmyōji who hunts elves.

According to Yasunori Katō, Subaru and Seishiro's respective designs pay homage to this character and the protagonist of the fantasy novel Teito Monogatari, who is widely credited with starting the "onmyōji boom" in Japan.

When designing Seishiro, Clamp wanted a strong contrast between his facade as a caring man and his cruel persona whenever he is wearing glasses.

[3] When production of Tokyo Babylon was finished, film director George Iida asked Clamp to help with a sequel movie in which Subaru and Seishiro would clash again.

[6] A common theme involves the series' fate; Subaru expresses no interest in the future of the Earth, but he and his counterpart are still drawn to Tokyo on the Promised Day.

[9] In Tsubasa: Reservoir Chronicle, Clamp originally intended Subaru to be the mentor of the protagonist, Syaoran, while searching for Seishiro.

However, they ended replacing him with Seishiro to avoid repeating the same pattern Tokyo Babylon and X had regarding these two characters.

[10] In the Tokyo Babylon original video animation, Seishiro was first voiced by Takehito Koyasu, who was replaced by Tōru Furusawa for the 1996 film X. Otoya Kawano took the role in the television adaptation.

[11] Hiroki Tōchi played Seishiro in Tsubasa: Reservoir Chronicle,[12] and the character will be voiced by Yūichirō Umehara in the television series Tokyo Babylon 2021.

[13] In English, Seishiro was first voiced by Dean Fenton in Tokyo Babylon, by Garrick Hagon in the feature film X, Dave Mallow in the X television series,[14] and J. Michael Tatum in Tsubasa.

[15] In Clamp no Kiseki, the writers described the character's past with Subaru revealed in flashback foreshadow an important event in his life.

[17][18] Due to the dark nature Seishiro hides from Subaru, the two can be regarded as the yin and yang as the former contrasts his the latter's kind self even when interacting about his job.

The Sakurazukamori assassinates a former enemy of the Sumeragi clan but his signature hand-through-the-chest style of killing is replaced with magical strangulation.

[49] Critics also commented on the character's return in X; Sequentalart praised his first fight against Kamui and for the way Clamp illustrates Seishiro's spells,[50] while Manga News felt his friendship with Fuma while causing an earthquake make the duo look as striking villain.

[52][53][54][55] In regards to Seishiro's history, Robin E. Brenner said in the book Understanding Manga and Anime, his bond is one of the most explicit in X, and that the romantic feelings between these two male characters are uncommon in Western stories.

Brenner stated Seishiro's unheard last words were meant to force readers to interpret them themselves, which is characteristic of manga series.

Manga News liked his role in Tsubasa because of his teacher-student relationship with the young Syaoran, the imposing manner he adopts, and that the character is more fully explored in this story arc.

[60] Seishiro's fight against the original Syaoran was praised for balancing the amount of exposition on which the narrative relies with the foreshadowing of other events.