Seigi Akoku

Built broadly and standing well above the height of his classmates, Seigi cuts a bulky figure among the students at his school. His clothing follows the standard boys' uniform, topped by an Inagaki cap, a round, stiff-brimmed hat of black fabric finished with a button at its crown. Stitched onto the front sits the katakana character 'デ,' read as 'de,' which is taken to abbreviate his role as a hunter of devils.

For close fighting he straps on spiked brass knuckles. The brawl with Yuko costs him his right eye, first wrapped in bandages and afterward hidden behind a dark eyepatch.

Seigi carries himself with discipline and steady resolve. When Yuko stormed the campus, he threw himself at the threat without hesitation, stalling her long enough for reinforcements to reach the school. His chief asset in any scrap is his own fists; quick enough to parry a transformed Yuko, he answers each opening with rapid flurries of punches.

Why he ends up among the Chainsaw Man Church faithful stays murky, since the story never clarifies whether club membership simply pulled him into that circle or whether he signed on by choice.

His introduction comes during Yuko's rampage through Fourth East High School. Seigi and two clubmates rush her together, and although his knuckledusters land genuine damage, Yuko overpowers the trio and ruins his right eye in the exchange.

Once the dust settles, he briefs student council head Haruka Iseumi on how Asa fared, and the club formally folds Asa into its ranks. A group outing to Tanashi Aquarium turns into a trap when an endless corridor seals everyone inside. Seigi correctly pins the phenomenon on a lurking devil, yet no one can find or kill it, so the students hunt for exits and pass the hours cooking fish. Their hopes spike when Asa produces a phone and collapse just as fast when she shatters it. The ordeal ends when Asa reshapes the entire aquarium into a spear and fells the revived Eternity Devil in one strike, leaving the club to explain matters to the Public Safety hunters who arrive.

Later, with the church leadership rounded up and held at the Tokyo Devil Detention Center, Seigi is sprung loose beside Haruka and Nobana when Asa and Fami overpower the guards. Branded fugitives, the three throw in with Fami's bid to recover the captive Chainsaw Man. The mission threads through a tense standoff with Takagi, a truce struck with Katana Man and the Nail Fiend, and the grim revelation that the dismembered hero is their own classmate Denji. Quanxi spares them, Takagi is devoured by his pseudo-chainsaw wife, and the group slips away to regroup. Seigi later stays behind with the Nail Fiend to guard the ruined apartment while the others chase down sushi. In the fallout of the Aging Devil's defeat, Public Safety captures and jails him once more, this time alongside Haruka, Nobana, and Katana Man.