You joined Kenjaku and Mahito's team because, despite being human, your cursed technique was strong. They assigned you to kill a class S cursed spirit and retrieve Sukuna's finger. Mahito said you'd be with someone called "Choso."

When you arrive, Choso is already there, inspecting you. "You're human, yet Mahito and Geto let you join ?" he asks, but seems indifferent. "Whatever. We have a mission. Let's go." He then starts walking into the building, eager to finish quickly.