Shizuma Kusanagi serves as a central figure, originally introduced as Daimon High's former K-Fight champion after losing his title to Ryoko Mitsurugi before the main narrative. He returns seeking a rematch, forging a rivalry interwoven with eventual romantic tension. His past includes a childhood encounter with elderly mentor Ryugan Higishikata, who taught him the principles of kamui—a method for manipulating fire-based energy (ki). Shizuma fused these teachings with his self-taught street-fighting skills, honed through years of brawling, creating the combat style kamui no ken. He later renamed it Hono no Tora ("Tiger of Flame"), wielding pyrokinetic abilities to rank among the school's strongest fighters despite lacking formal training.

His personality blends a rough, occasionally cruel exterior with consistent softness toward Miyuki Onizuka (Hiten Shrine caretaker's granddaughter), devoted supporter Sara Himekawa, and rival Ryoko Mitsurugi. During their climactic final battle in the manga's sixth volume, he openly confesses romantic feelings for Ryoko, culminating in an emotional embrace and concession of victory. Beyond combat, Shizuma demonstrates musical talent with guitar and piano, stemming from his family background, and frequently rides a motorcycle. His appearance and fighting style draw inspiration from figures like Kyo Kusanagi (*The King of Fighters*) and, in manga artwork, Donnie Yen.

Within manga continuity, Shizuma establishes a personal fan club due to avoiding school clubs. His evolution involves clashes with criminal organizations and student council conflicts, notably employing nunchakus against Ryoko in their decisive duel. The anime adaptation retains his core traits but shifts his role: entangled in an interdimensional conflict involving Solvania, his development remains secondary to the central plot. Here, his kamui abilities are framed as rare yet recognized phenomena within the K-Fight system. Light novels—centered on a teacher protagonist—feature Shizuma as a supporting character with consistent traits, though his narrative presence lessens.