Nanase Shun navigates the demanding environment of Seitei Gakuen, Tokyo’s elite private academy, as a student in Class X—infamously labeled Class 3-E or III-E. This class functions as a repository for academically challenged students, where Shun stands among the six disruptive core members dubbed "B6" (Baka 6), notorious for driving previous teachers to resign through stress-induced health crises.

He maintains an intense schedule, juggling part-time employment with his role as bassist and leader of Visconti, a popular indie rock band active across Tokyo’s live-house circuit. These relentless commitments eclipse any opportunity for academic focus. His demeanor projects cool strictness, demanding high standards from himself and others, particularly in financial matters. Physically, he measures 183 cm tall, weighs 72 kg, and possesses blood type A.

Within the VitaminX Addiction narrative, Shun faces teacher Minami Yuuri’s challenge to grasp the purpose of studying and prepare for university entrance exams. His journey unfolds alongside fellow B6 members as they confront academic expectations. Musically, he performs the ending theme "Yuujo(ULTI∞MATE)VOLCANO" with B6 peer Kiyoharu Sendo for the OVA’s second episode and features on a dedicated character song CD within the franchise’s music offerings.