Yukio Tanaka, often called Koyuki, is the protagonist of the series. Initially an unremarkable and passive teenager, his life takes a dramatic turn as he evolves into a talented and emotionally resonant guitarist. Though timid and easily pushed around—perhaps a subtle reflection of Japan's reserved, conformity-driven culture—Koyuki finds his voice, both literally and figuratively, through music. As the final member to join BECK, he becomes the band's second guitarist and a vocalist known for his stunningly beautiful voice, often featured in their more soulful, slower tracks. He plays a Fender Telecaster.