Cool, a Cerberus-like demon, serves as Setsuna’s steadfast companion in the Black Book storyline, fighting alongside him in duels against hostile entities during their battles. His role emerges when Setsuna’s younger brother, Nagahisa, is abducted by an army of Jack Frosts, sparking their perilous journey into the demon world to reclaim him.

In the manga adaptation, Cool appears shortly after Setsuna obtains the Deviliser, a powerful weapon, joining forces to repel a demon assault on his home. Together, they venture into Makai, a realm embroiled in chaos, where Cool confronts angels, demons, and other adversaries. His combat prowess proves vital as Setsuna seeks reality-altering artifacts, solidifying Cool’s position as an unwavering ally.

Cool’s origins intertwine with the ancient conflict between demons and angels, his presence a constant amid Makai’s war-torn landscapes. While the games highlight his martial contributions, the manga delves deeper into his narrative integration, including alliances with figures like Mirai Kaname, a protagonist from a parallel storyline. Across both media, Cool retains his Cerberus-inspired design and combat-focused abilities, ensuring consistency in his portrayal.

Exclusive to the core games and manga, Cool’s narrative revolves entirely around aiding Setsuna’s mission, prioritizing loyalty and battlefield support over personal evolution or divergent arcs.