Atsushi Ryuuzaki leads the Matsubara yakuza group. He has russet hair, long thin eyebrows above small eyes, and styled facial stubble beneath his nose and on his chin. His typical attire consists of suits, frequently including a dark faded green jacket and pants secured by a brown belt, worn over a dark gray collared shirt and pale blue tie, complemented by brown laceless dress shoes.

Ryuuzaki interacts directly, often shifting blame onto others. He exhibits hypocrisy, looking down on Yashiro for his background and activities while engaging in similar conduct. Analytically minded and reserved, Ryuuzaki values logic and independence, struggles with emotional expression, and isolates himself for work or reflection. He maintains guarded boundaries to protect his autonomy, resulting in isolation and difficulty forming connections.

He rose to become Wakagashira (second-in-command) of the Shinseikai syndicate. Ryuuzaki shares a sworn brotherhood with Yashiro within the organization, knowing him since age 21 when Yashiro frequented a mahjong parlor affiliated with Ryuuzaki's Matsubara group. Their relationship evolves to reveal Ryuuzaki's concealed love for Yashiro. Demonstrating loyalty, he endured torture after capture by Hirata for refusing to assassinate Yashiro, remaining steadfast even after Hirata kidnapped his female companion. When Yashiro rescued him, Ryuuzaki hid his injuries during their escape to avoid appearing vulnerable.

His given name "Atsushi" combines "篤" (deep, true, sincere) and "士" (samurai, warrior, gentleman). His surname "Ryūzaki" means "dragon" (竜) and "cape/peninsula" (崎).