Kei Sugihara operates as a regional boss in the Sakuragi family yakuza. He sports shoulder-length blond hair often partially tied in a bun, green eyes, and a distinctive lip ring on his lower right lip. His typical outfit is a long-sleeve shirt, faded dark blue jeans, and black sneakers. Born September 1, he stands 1.75 meters tall at age 23 with blood type AB. For better or worse, Kei possesses an honest and emotionally expressive personality, making him a frequent target of teasing. He demonstrates deep loyalty to Tōru Kirishima, whom he deeply respects. His capacity for empathy is noted as remarkable, often forming intense attachments that trigger emotional outbursts like shouting or crying. Watching movies is one of his documented hobbies. Five years before the main events, Kei was a disowned shoplifter disregarded by adults who only valued his stealing skills. His life shifted when he attempted to steal from a yakuza-protected antique shop. Kirishima caught him and exposed his lie after Kei inadvertently mentioned the store's lotus-designed teacup. Rather than punishment, Kirishima took Kei to the Sakuragi estate and instructed him to prepare tea with that same cup. Kirishima's praise of his tea-making caused Kei to break down and plead to be taken in, leading to his permanent residence with the family. As shateikashira (top follower), Kei operates directly under Kirishima. He frequently endures the brunt of Kirishima's frustrations, suffering pranks like having his hair styled femininely or drinks poured on him, escalating to physical confrontations during Kirishima's angrier moments. Despite this, their relationship evolves into vitriolic mutual reliance, with Kei viewing Kirishima as an irreplaceable brother figure. Kei's responsibilities expand when tasked with temporarily caring for Yaeka Sakuragi during Kirishima's absences. He actively attempts to bond with her, though initial efforts like shared meals result in awkward silence. Introducing her to his anime and film collection leads to an emotional viewing of the tear-jerking "Mii-chan" series. Recognizing Yaeka's stronger bond with Kirishima, Kei offers to share stories about him instead. During an outing to Fuyutsuki Park, he facilitates Yaeka's first friendship with a girl named Sarah. After Yaeka is taken hostage and sustains a concussion, Kirishima leaves out of guilt, instructing Kei via letter to assume caretaking duties. Witnessing Yaeka's distress, Kei accompanies her to search for Kirishima, locating him at Fuyutsuki Park. He confronts Kirishima, insisting protecting Yaeka requires becoming stronger, not abandoning her. This intervention proves pivotal in convincing Kirishima to return, underscoring Kei's growth into a voice of resolve during crises. His surname combines "cedar" (杉) and "field, plain" (原), while his given name means "favor, benefit" (恵).