Motochika Chosokabe, the pirate leader of Shikoku, commands fear as the "Demon of Shikoku" or "Sea Devil of the West." His striking appearance features spiky white hair, a prominent eyepatch over his left eye, and a predominantly purple outfit highlighted by an extremely short coat worn cape-style over his shoulders, leaving his chest exposed. He wields an anchor-tipped spear with remarkable versatility, detaching the anchor for ranged attacks or riding the spear staff like a surfboard for aerial mobility. His combat style incorporates fiery abilities, cementing his elemental association with fire.

His personality blends fierce loyalty with a roguish, adventurous spirit. He prioritizes exploration and treasure hunting over territorial conquest, embodying a lovable rogue. Central to his character is his profound bond with his crew; they address him as "aniki" (big brother) as a sign of respect and camaraderie, and he reciprocates by calling them collectively "mateys." This relationship defines his actions, driving his unwavering protectiveness toward his subordinates. Conversely, deception or harm aimed at his crew or allies ignites intense rage, making betrayal his primary berserk button.

His character arc is fueled by vengeance and loyalty. After Hideyoshi Toyotomi's death, Shikoku suffers an attack by forces Motochika believes are led by Ieyasu Tokugawa, resulting in the apparent annihilation of his crew and his forced flight. Consumed by grief and rage, he allies with Mitsunari Ishida's Western Army on the advice of his rival, Motonari Mori, seeking revenge against Ieyasu, positioning him directly against the Tokugawa faction. He later uncovers Motonari orchestrated the attack on Shikoku to manipulate him. This revelation triggers a profound crisis; in some narratives, the shock and guilt over being deceived and targeting an innocent Ieyasu drive him to a moment of despair where he willingly allows Motonari to strike him down, highlighting his susceptibility to profound regret when his trust is exploited.

His interactions forge key dynamics. His significant rivalry with Motonari Mori stems from competing maritime control and contrasting philosophies—Motochika values camaraderie, while Motonari views soldiers as expendable pawns. Despite antagonism, Motochika regards Motonari as a worthy opponent, though this respect is not reciprocated. His relationship with Ieyasu Tokugawa shifts from initial vengeance-seeking toward mutual, albeit strained, respect upon learning of Ieyasu's innocence. He shares a friendly, competitive rapport with Masamune Date, often exchanging challenges. He also engages in a situational rivalry with Tsuruhime due to their shared naval expertise, challenging her to races in certain storylines.

Notable traits include his passionate catchphrases like "We're demons, eat 'em up and swallow 'em whole!" or "The scream of the soul, shaking your own call to rebellion!". He employs elaborate traps in his fortress and naval-based war machines, including a spider tank-like vehicle called Akatsukimaru. Despite his flamboyant and occasionally impulsive demeanor, he possesses a strong sense of honor and demonstrates the capacity to acknowledge his errors, particularly in interactions with Ieyasu after learning the truth about Shikoku.