Jellyfish is a ballpoint pen composed only of a body and an ink tube. The design is based on a simple mechanism, derived from the flexibility of an ink tube that is made with polyethylene (PE). The wave-shaped ink tube in the groove of the grip works as an operating button. When a user holds this pen, the ballpoint emerges automatically due to expansion, and when releasing the pen after use, the ballpoint naturally retracts due to contraction. Therefore, Jellyfish helps users break away from the existing ballpoint pen operating behaviors for easier use and maintenance.