Ryūsei Nagamine is a large man with black hair and brown eyes, typically dressed in a red T-shirt, blue jeans, a cap, and sneakers. His demeanor is laid-back yet cautious, especially regarding personal disclosures, and he collects computer accessories like keyboards and mice as an otaku.

He joined Fox One as the fourth recruit after the original members retired, aiding in rebuilding the team for competitive gaming. During Fox One's participation in the Zaxelion Bit Technica League, initial struggles prompted Ryūsei to engage from his perspective as a former fan. His critical advice spurred strategic reevaluation and renewed efforts toward victory, marking his transition from an outsider to an integrated member invested in the team's improvement.

The name Ryūsei translates to "meteor" or "falling star," while Nagamine combines "long" and "ridge."