Chiba Tsunemi, often called simply Chiba or Tsune, is the vocalist and MC for the fictional band BECK. At the start of the story, he is fifteen years old, and by the end, he is twenty. Chiba is a founding member of the group, recruited by the guitarist Ryusuke after the dissolution of his previous band.

One of Chiba's most defining traits is his energetic, aggressive, and outspoken personality. He is cheerful, often acts impulsively, and serves as a primary hype man and atmosphere maker for the band, frequently controlling the crowd's response during performances and acting as a commentator within the group. His appearance is marked by his signature afro hairstyle, a visual trait inspired by Jack de la Rocha of the band Rage Against the Machine.

Chiba's motivation is deeply rooted in his family. He lives with his mother and an older brother who has a mental disability, and a primary reason for his desire to succeed as a musician is to provide for them. This sense of responsibility extends to his friends. Despite his loud and sometimes combative nature, he has a strong moral core, particularly despising bullies and protecting the weak. This protective instinct is shown early on when he intervenes to stop Koyuki from being bullied in middle school, an act that decisively ends the harassment. Chiba's past is not one of inherent toughness; he was once a weak crybaby who learned karate to gain strength and self-control.

Within the narrative of BECK, Chiba's role is that of the passionate frontman and a key source of the band's raw energy. He is not only the lead singer but also handles the MC duties and rap vocals, which give the band a distinct, funky, and fast-paced vibe compared to the more melodic songs sung by Koyuki. His creative contribution is significant, as he is the one who proposes the band's name, BECK, which the group adopts as a temporary title that ultimately sticks.

His relationships with other band members are central to his development. While he gets along with everyone, he forms a particularly complex bond with the protagonist, Koyuki. Chiba initially saves Koyuki from bullies and is a supportive bandmate. However, a significant portion of his character arc involves a struggle with self-worth. He experiences doubt about his own place in the band, feeling a need to prove he is an essential part of BECK. This insecurity is exploited during a plot by an antagonist, causing a temporary rift where Chiba distances himself from Koyuki. This conflict is resolved when Chiba privately expresses his deep admiration for Koyuki's talent, calling him one of the few people he truly respects and acknowledging that Koyuki's voice will make him a huge success. A key moment in their relationship occurs during a major festival performance when Chiba fights his way through security and the crowd to rejoin the band on stage, solidifying his commitment. Ultimately, Chiba's development is about overcoming his personal insecurities and recognizing his value as an integral part of the group, with other members noting that it was Koyuki who made Chiba stop running away from his own feelings.

Chiba possesses several notable abilities beyond his musical talents. As a vocalist, his style is unique, incorporating rapping and freestyle battle skills, and his listening tastes include influential groups like Run DMC and The Roots. His charismatic and spirited showmanship is a powerful asset during live performances, capable of salvaging a bad show or capturing the audience's attention through sheer force of personality. Outside of music, his training in karate makes him the band's primary physical enforcer, the first to step up when a confrontation turns violent. While not his main focus, his physical prowess and willingness to fight are recurring aspects of his character.