Dōen is a monk and self-proclaimed doctor serving among prisoners exiled to Tsushima Island to form a disposable force against the Mongol invasion. His exile stems from an unspecified criminal past where he used medical knowledge to harm others; seeking atonement, he became both monk and healer. Despite his youth, he possesses advanced medical skills, including medicine concoction and wound suturing, making him the group's primary healer.

He exhibits a stoic personality, speaking minimally and maintaining a stern expression. His unwavering dedication focuses on treating injuries sustained by fellow exiles and Tsushima defenders during combat, prioritizing patient safety above his own. Witnessing the death of non-combatants during the conflict profoundly impacts him.

In a critical moment under attack, Dōen sacrifices himself to protect his patients, physically shielding them with his body and taking a fatal gunshot wound. This selfless act prevents immediate harm to those under his care but costs him his life. His death deeply affects his comrades, particularly triggering a vengeful response from the archer Hitari. Dōen's background as an atoner and his final act underscore his commitment to redemption through healing and protection.