Kaz Walker, known as Kazuya Aoshima in the original Japanese version, is a main protagonist in the LBX anime series. He is a student and an avid LBX player who shares a close, long-standing friendship with the primary protagonist Ban Yamano and their friend Amy Cohen, having been close with them since childhood. Kaz is very knowledgeable about LBX and frequently spends time at a local shop owned by a woman named Maya, which serves as a common gathering place for him and his friends.

In terms of personality, Kaz initially comes across as friendly and well-meaning, but he can also be cynical and quick to show a lack of confidence when faced with challenges that seem overwhelming. He tends to give up easily on difficult matters, yet this insecurity contrasts sharply with a fierce protective instinct. He does not hesitate to act harshly or confront those who threaten or harm his friends, demonstrating a deep loyalty that defines his core motivations. His primary drive throughout the story is to support and fight alongside his friends, using his strategic mind and skills as an LBX battler to help them overcome the various conspiracies they face.

As the story progresses, Kaz plays a key role as a member of the primary group opposing the antagonist organization known as the Innovators or the New Dawn Raisers. He experiences significant personal trials early on, such as when his first LBX, Warrior, is destroyed by an opponent. This event leaves him depressed, and he later falls into a trap set by the Innovators, who brainjack him into piloting an LBX called Egypt against Ban. After Ban wins the battle and frees him from this control, Kaz is recruited for a mission that ultimately leads to him receiving a new LBX named Hunter. He continues to evolve as a battler, later piloting machines like Fenrir and Achilles Deed.

Kaz's relationships are central to his character arc. His bond with Ban and Amy is the foundation of his actions, and he also develops a notable rivalry-turned-friendship with another skilled battler, Jin Kaidou. Kaz initially acts harshly toward Jin due to the latter's alliance with a villainous agenda, but he eventually accepts Jin as a comrade after Jin proves his loyalty to Ban. In the sequel series, LBX W, Kaz is captured and brainjacked once again, but an accident short-circuits his control collar, granting him free will. He uses this to secretly work against his captors, even adopting a new, more muscular appearance, before reuniting with his friends and rejoining their fight. His abilities are notable for his expertise in long-range shooting and tactical
combat, often earning him a rate bonus when his LBX uses a two-handed gun.