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UoD Logo By ShizukuTsukishima Part of the Universe of Dimensions continuity.
Biographical information

Fire Nation


Fire Nation

Physical description


Hair color


Eye color


Personal information
Weapon of choice


Fighting style(s)



Kouichi, Aang, Iroh (formerly), Yuko, Sugimura, Shizuku


Hide, Azula, the Dai Li, dark spirits, General Valo, Haku, X3

Chronological and political information
  • Soldier (formerly)
  • Body guard

United Forces (formerly)

First appearance

Universe of Dimensions, Prologue

Seiji is one of the main protagonists in Universe of Dimensions. In the bending dimension, he was the most talented soldier of the United Forces but also the most rambunctious. With an inherent disregard for authority, Seiji was often lost in his own angst and turmoil. Kouichi, Seiji's father, was a top scientist who was ridiculed for his ideas and disappeared through his rift gate invention, after trying it out and never returning. Avatar Aang chose Seiji to be Yuko's protector, who must now work to ensure the safety of Aang's daughter.


Early life

Seiji's life was hard after his father vanished. With no other family to take him in, Aang made arrangements to send Seiji to the National Fire Academy for Boys. There, they hoped the boy would become a grand soldier, but more importantly, he would be surrounded by friends.

At the National Fire Academy for Boys

However, Hide constantly bullied Seiji.

Escape from Republic City

After some time in the United Forces, Seiji and his unit were placed in charge of saving hostages from the Dai Li. Seiji disobeyed orders not to engage the enemy and entered the building anyway. Inside, he found all the hostages dead and overheard the Dai Li planning an invasion.

His superior instead blamed him for the hostages' deaths, confiscated his armor and placed him under arrest. Seiji pleaded for Aang to listen to him, but the Avatar refused to believe him until it was too late. With the invasion, Seiji discovered that his superior was a traitor and after a long Agni Kai, he killed the traitor and saved Aang's family while increasing the strength of the defense. With this, Aang promoted Seiji to Yuko's protector and sent them to the non-bending dimension with her.



Seiji demonstrates great skill in traditional firebending combat. He can maintain his fire streams for a period of time for feats such as propelling himself through the air. He can also perform more advanced techniques such as the breath of fire. The raw strength of his firebending is also considerable, able to offset a large and point-blank explosion unharmed. His control is also very fine, as he is able to form a sleek dagger for intimidation and the likes.


Seiji's rebellious and troublesome nature often caused him much turmoil back in the non-bending dimension.

Ironically, it is this very personality that almost instantly makes him one of the most popular students at Lincoln High School, making cheerleaders and other students love him. Unlike most other students, he doesn't immediately fall to its benefits and tries to push himself away from them. He becomes confused, realizing that despite his efforts, he only continues to rise in the social hierarchy. In a normal situation, Seiji is laid back and not one to openly display his emotions. He does, however, come alive on the battlefield, always thirsting for the victory that will somehow imbue his life with true meaning. Seiji shows signs of a self-loathing complex, seeming to stem from the day his father vanished. Even to this day, Seiji will still wake up in the night, due to the fact that was the time his father would return from work. Earlier in the series, he is shown to be very paranoid, such as assuming a crying baby or a dog could be considered a threat.




Kouichi is/was Seiji's father. Seiji loved his father very much and was very upset when he disappeared. He still keeps a framed picture of him and his father hugging.



Initially, Seiji was unsatisfied with his orders to watch over and protect Yuko, but he chose to follow those orders and became extremely overprotective of Yuko. At first, the two are subject to bickering with one another, and it has become one of Sugimura and Shizuku's many duties to break up fights between the two. This makes their relationship practically brother and sister, like they pretend to be, although it is more like a sibling rivalry relationship between the two of them. This may be partially due to the fact that the two of them have clashing personalities; Yuko's being more honest and optimistic, while Seiji displays more of a trouble-making, rebellious mind. But as time goes on, they become more understanding of each other, and they care for each to the point that they see each other as family.

Sugimura and Shizuku

Sugimura and Shizuku are like parental figures to Seiji and two friends. They may have more of a parent/son relationship due to his presumably deceased father. Sugimura and Seiji tend to have very deep conversations and are both very commutative with one another with advice.


Universe of Dimensions

Universe of Dimensions 2

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For the collective works of the author, go here.

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