Mutsuki Naitō leads the professional esports team "SLEEPING OWL" as its ace player under the handle "ROX." He commands widespread respect and awe for his exceptional strategic prowess and ability to secure victories under intense pressure, often eliminating entire opposing teams as the sole survivor. His distinctive pre-match ritual involves consuming retort pouch curry through a straw.

He thoroughly investigated the background of Shun Tokinoya, the protagonist of rival team "FOX ONE." Mutsuki demanded Shun abandon all personal attachments, including family responsibilities, believing such total sacrifice was essential for peak competitive performance. He directly challenged Shun's motivation—supporting his sister Mio's rehabilitation—arguing it inherently limited his potential. Shun's unwavering rejection of this demand created a significant conflict, rooted in Mutsuki's conviction that true excellence requires undivided commitment.

Mutsuki developed a complex rivalry with Shun, viewing him as a uniquely "worthy opponent" capable of matching his skill. During competitions, he demonstrated a tactical ability termed "Combat Clairvoyance," allowing him to anticipate opponents' moves, though its origin—strategic analysis or innate capability—remained ambiguous. After "FOX ONE" suffered consecutive tournament losses, Mutsuki temporarily dismissed Shun as unworthy. Ultimately, he acknowledged Shun's resolve following their final confrontation, where Shun prioritized his team and family over solitary ambition.