Kevin Valentine serves as a Player and Equipment specialist in the Lucia region, directing Tremolo Technologies. This organization specializes in analyzing mechanical debris from Equipment destroyed during conflicts with the Earless. His technical expertise extends to constructing combat machinery, most notably the dual-piloted mecha The Crimson Belle—affectionately nicknamed "Sue"—which he engineered for joint operation with Bilin Valentine.

Visually, Kevin appears as a young adult with short, tousled brown hair, consistently clad in a white coat. A decade before current events, he and Bilin were traveling to join Project Freedom ("the Fest"), a large-scale operation intended to eradicate the Earless. The mission collapsed catastrophically when Jimi Stonefree betrayed the cause, triggering widespread destruction across Lucia. As the project’s primary sponsor, Lucia bore public blame for inciting the war, resulting in its citizens' displacement. This failure drove Kevin into self-imposed isolation within his room for four years.

He emerged upon witnessing Echo Rec attempting repairs on damaged Equipment. This prompted his first departure from seclusion since the disaster, leading him to assist Echo. When recognized, Kevin confessed his reluctance to pilot Sue alongside Bilin, fearing for her combat safety. He explicitly prioritized her well-being over Lucia’s strategic future. Later, he and Bilin engaged in a mock battle against Mu and Echo, securing victory. Bilin permitted Mu and Echo to leave afterward, advising them to gather intel on Jimi from other Players.

Kevin’s partnership with Bilin Valentine centers on his role as her Equipment manager. They operate as a battle couple, co-piloting Sue in combat. Their dynamic reflects a generational parallel to Mu and Echo—pairing a female Player with a male Equipment handler. Both frequently weave English phrases into their speech. After the main conflict’s resolution, Kevin ascended as the King of Londinium.