Seita (晴太) is the adoptive son of Hinowa 日輪 and the biological son of a courtesan of Yoshiwara, who died after giving birth. As a baby, he was led to the outside world in the care of an old man by Hinowa.
Seita has borwn, neck-length hair and brown eyes. He can usually be seen wearing an olive yukata.
As described by Otose お登勢, he is clever, honest and learns quickly. He's able to adapt to new situations as evidenced by his ability to make a living through pickpocketing alone but also earn legitly by honest work.
He has a kind and strong heart as even after learning Hinowa isn't his biological mother, he stands firm and claims it enough that she risked her own safety to protect him to be considered his mother.
Seita first appeared trying to pickpocket Sakata Gintoki 坂田 銀時 but ended up caught. He was then taken to Snack Otose スナックお登勢, where he revealed that the old man taking care of him passed away 3 years prior and is now gathering money to see the number one courtesan of Yoshiwara, Hinowa, who he believes to be his mother. Hearing his story, Otose offered him to work for her.
Weeks later, he snuck in Yoshiwara, together with Kagura 神楽 and Shimura Shinpachi 志村 新八 but was quickly discovered by the Hyakka 百華. After Tsukuyo 月詠 seemingly killed him and the Yorozuya 万事屋, she led them to an escape route. However, they were interupted by Kamui 神威 and his subordinates, who managed to kidnap Seita to use for blackmailing Housen into letting Kamui see Hinowa. He managed to escape in the commotion caused by the fight that broke out between the two Yato clansmen. He was later found by Kamui and led to Hinowa's chamber, where Housen caught up to them and revealed that Seita's real mother had passed away giving birth and Hinowa escaped to the outside along with him, leaving him in the care of an old man before being recaptured. The news didn't faze Seita as he continued trying to break down Hinowa's locked door. After Gintoki also arrived at the scene and began to fight Housen, Seita, after some convincing, carried his mother out. Before Housen could stop him, the Hyakka intervened and gave him an opening. Promted by Hinowa and his own desire to help in the fight against the Night King, Seita goes searching for the controls of the artifical roof that stand between Yoshiwara and the sky. In the end, after some hardship, he manages to open the hatch and shine light over the city and Housen, who ultimately dies of the sudden exposure to the light. After everything settled down, Seita went to live with his mother and started working at an Adult Toy Store.
Some time later, while Tsukuyoo and Gintoki investigate the string of illegal drugs, he, along with Kagura and Shinpachi learns of Tsukuyo's past with her master. When Jiraia atempts to burn Yoshiwara, he helps stop the fire from spreading along with the citizens of the city. In the end, Seita, Hinowa, Kagura and Shinpachi use and spy on Gintoki to help Tsukuyo relax but are eventually forced to join by a drunk Tsukuyo.