Abe no Sousei is the stoic captain of the Yamainu Squad, charged by the government with capturing Orochi's vessel. Born to master exorcists, he was separated from his parents at birth and raised in isolation without toys or companionship, resulting in a reserved personality and limited social abilities.

As a candidate to become Orochi's vessel himself, Sousei joined the Yamainu Squad and trained under Taiko, wielding the Abe family's ancestral sword. He soon forged friendships with Tenka and Kiiko. Influenced by Tenka, Sousei shifted his self-perception from being merely a pawn in Orochi's capture to embracing Tenka's dream of becoming a national hero, significantly reevaluating his life's purpose.

He maintains key relationships as Tenka's childhood friend and Soramaru's swordmaster. His interactions reveal contrasting facets: he criticizes Tenka's solitary nature, stating, "You've always stood above others... Disappear. High, mighty, and alone," yet offers compassion to Soramaru, advising, "Who said crying was a sign of weakness? Embrace those memories and cry, before you forget." During critical moments, he prioritizes the mission, commanding Kiiko, "We can’t have him interfere. Get Tenka away from here."

Sousei stands 174 cm tall, weighs 59 kg, and has blood type A. Born on October 25 under the Scorpio sign, he collects stamps. His food preferences favor karashi renkon while disliking wasabi and pointless things.

This depicts his development from an isolated individual to someone valuing connections and shared purpose, while maintaining his disciplined role within the Yamainu Squad.