Description
Shu Kurenai stands as a central figure in the Beyblade Burst narrative. Initially introduced as a highly skilled Blader and member of the Supreme Four, he claimed runner-up status in the previous year's National Tournament with his Beyblade, Storm Spryzen Knuckle Unite. His appearance features shaggy white hair, bright crimson eyes, and a notable scar over his right eye inflicted during a battle with Lui Shirosagi; this scar is typically concealed by his hair but becomes visible when swept aside and reportedly glows red during moments of intense emotion. His attire evolves across seasons, often including a pink dress shirt, black vest, signature red fingerless glove, and variations of trench coats or high-collared vests. Distinct outfits mark his Red Eye persona in Evolution, featuring a voice-altering mask and elongated hair.

Combining natural talent with intense dedication, Shu is described as a "genius blader" who trains rigorously. Typically calm, reserved, and observant, he displays ambidexterity in Beyblade launching and daily activities like cooking—a skill honed out of necessity due to his parents' frequent absence. While initially perceived as aloof, he maintains deep loyalty to close friends like Valt Aoi. This loyalty fuels a stubborn streak, notably causing him to ignore medical advice to rest a shoulder injury sustained during training, prioritizing his promise to battle Valt.

A significant transformation occurs in Beyblade Burst Evolution following consecutive losses: first to Lui Shirosagi, which shattered his Beyblade and broke a pact with Valt, and later to Free De La Hoya after joining the American team Raging Bulls. These defeats, coupled with manipulation by the Snake Pit Organization led by Ashtem, trigger his descent into the antagonist persona "Red Eye." Adopting a ruthless approach, he prioritizes strength above all else, willingly destroying opponents' Beyblades and severing ties with former allies. This path culminates during the "Requiem Project," where he is tasked with mentally erasing Valt to earn Spryzen Requiem 0 Zeta. Wielding this Beyblade corrupts him further, leading to literal possession by the Bey's spirit and a complete embrace of aggression.

His redemption occurs during the International Blader's Cup finals against Valt. Valt's victory breaks Spryzen Requiem's control, restoring Shu's original personality and facilitating reconciliation. This experience profoundly shapes his later roles. In Turbo, as the new owner of the Raging Bulls, he mentors Fubuki Sumiye and intervenes to help Aiger Akabane resist corruption in his Beyblade resonance, explicitly drawing parallels to his own past. His wisdom and empathy are further highlighted in Surge, mentoring Lain Valhalla, crafting the Lightning Beyblade World Spryzen Unite' 2B to aid Valt, and partnering with Lain as runners-up in the Ultimate Tag Series. He continues competing in subsequent seasons, evolving his Beyblade to Astral Spryzen Over Quattro-0 in QuadDrive and later to Bolt Spryzen Xanthus-Q Quattro-Q+Jaggy-1 in QuadStrike, where he also assists the WBBA in researching ancient ruins and elemental powers.

Age references place him at 11 during Burst and Evolution, approximately 13 in Turbo, and around 15 in later installments like QuadStrike.