Ichirou Seii (勢威 一郎, Seii Ichirō) is a senior guardian pilot and executive officer/battle commander aide to Captain Kobayashi. Seii later becomes a dedicated gardes pilot and had Yuhata Midorikawa take his place as XO to Sidonia Command.

Personality & Character

Seii is a white haired senior guardian pilot and executive officer (XO) to Kobayashi during military operations; he's also an instructor at the SDF academy. It's Seii's responsibility to delegate all officers to follow is command and complete the mission(s) at the CIC (combat info center); he needs Kobayashi's approval for major tactical decisions. While a decent tactician, Seii realized there are those much suited for the role as XO than him; he would later get reassigned as a gardes pilot to let Yuhata Midorikawa succeed him (by his own recommendation). While not at the CIC, he teaches various courses about tactics and the gauna at the academy to groom future guardians. As one of the top pilots, Seii is one of the few pilots that survived the 5th Gauna Defense War.


Since the beginning of the series, Seii is the Commander's Aide to the Captain. He assists in battle and directs personnel. When Gauna 487 was encountered on the mining mission, he was struck numb by his first encounter with a Gauna. In the diagonal acceleration to avoid Gauna 487's attack, he was horrified by the casualty reports, but it would have been thousands of lives or complete annihilation if 487 boarded Sidonia. Soon he leaves his position to Yuhata Midorikawa to become a combat pilot. Leader of the Seii squad and designated unit 026, Seii is initially assistant commander and Brilliant OX of Sidonia before passing his post to another younger and just as brilliant - Yuhata Midorikawa. Seii is one of the more serious and experienced older Garde pilots and had many heated fights and arguments with the captain of Sidonia - Kobayashi, and with his is assistance gets Nagate Tanikaze to show his true self and distinctive fighting style with the Garde Model #17 Tsugimori. In the manga, Seii wears a distinctive vintage helmet that covers most of his face. He participates in many battles, most notably the attack on the Large Mass Union ship. His team almost died off in the attack, which lead to 38 deaths out of the 48 man squad, but over 200 Gauna were killed and Sidonia was saved.


Seii is a tall man with white hair and blue eyes. He wears the typical crew member uniform until he becomes a Garde pilot, when he exchanges his uniform for a skin suit.


  • The name Ichirou means "one" (一) (ichi) and "son" (郎) (rou).
  • Ichirou's surname Seii means "power" (勢威).


  • Seii is the one who initially spreads the rumor about Samari Ittan photosynthesizing with male pilots who rack up high kill counts to boost pilot morale. It is implied that he eventually enters a relationship with Samari and fathers several children with her.



Knights of Sidonia Characters
Gardes Pilots

Nagate Tanikaze | Izana Shinatose | Shizuka Hoshijiro | Honoka Sisters | Mochikuni Akai | Hinata Momose | Kashiwade Aoki | Izumo Midorikawa | Eiko Yamano - Toutarou Yamano| Samari Ittan | Tonami | Kouichi Tsuruuchi | Ichirou Seii | Norio Kunato | Kaoru Hazama | Ryouhei Kasuga | Kujira Negi | Hamagata | Hashine | Suzuki

Sidonia Command

Yuhata Midorikawa | Ryouko Takahashi | Ichirou Seii | Ochiai Clone

Immortal Ship Committee

Kobayashi | Lala Hiyama | Hiroki Saitou | Yure Shinatose | Ochiai

ET Research Center

Numi Tahiro | Yure Shinatose

Toha Heavy Industries

Sasaki | Shinsuke Tanba | Shijimi

Kunato Developments

Norio Kunato - Mozuku Kunato


Teruru Ichigaya


Tsumugi Shiraui - Kanata

Gauna 487 | Gauna 491 | Gauna 492 | Gauna 493 | Benisuzume | Placental Hoshijiro | Ocarina | Gauna 541 | Large Mass Union Ship | Lem Gauna Wall | Lem VII Gauna | Aulos
Knights of Sidonia
Anime Season 1 | S1 compilation movie | Season 2 | The Star Where Love is Spun (movie) | Season 3
Subjects & Topics Sidonia | Gauna | Gardes | Technology of Sidonia | Characters of Sidonia |
Manga Volume 1 | Volume 2 | Volume 3 | Volume 4 | Volume 5 | Volume 6 | Volume 7 | Volume 8 | Volume 9 | Volume 10 | Volume 11 | Volume 12 | Volume 13
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