Junpei Ryuzoj is a nineteen-year-old martial artist from Japan who finds himself transported to a fantasy world against his will. Having failed his college entrance exams, his primary ambitions back home were to pursue a path in martial arts, and he brings considerable physical prowess to the group of stranded individuals. In terms of personality, Junpei is loud, impatient, and direct, believing that the most efficient solution to any problem is often a physical one. He is famously obsessed with curry rice, to the point that he knows how to cook it himself, and his frustration at being unable to find this specific dish in the magical realm is a constant source of irritation for him. He is also a big fan of the movie star Airi Komiyama, for whom he carries a deep infatuation, though he remains largely oblivious to the romantic feelings of others, including those of the elf Celcia Marie Claire with whom he constantly bickers. His signature exclamations often include variations of "Junpei Ryuzoj is here!" and complaints that "this is why I hate fantasy!".

Junpei's primary motivation is simply to return to Japan, and the only method available requires his group to collect five spell fragments imprinted on the skin of various elves. This mission defines his role in the story, as he serves as the muscle and primary enforcer of the group. His approach to obtaining these fragments is notoriously aggressive and straightforward, leading to the group's reputation for forcibly stripping any elf they encounter, a task he enthusiastically undertakes regardless of the target's age, gender, or even species, as long as they possess long, elf-like ears. Komiyama acts as the group's strategist, often manipulating Junpei into executing dangerous plans with her charm, while the weapons-obsessed Ritsuko Inoue drives their Type 74 tank and provides long-range support. His relationship with Celcia is particularly noteworthy; despite their constant arguments and mutual frustration, he is often the first to leap to her rescue when she is in genuine danger. Over the course of his adventure, Junpei's already impressive fighting abilities escalate to seemingly superhuman levels, as demonstrated when he manages to fight aliens without being touched or uses a fishhook to catch a live shark. This development continues in the second part of the story, where he has become an undefeated martial arts champion in the human world before being resummoned, and he eventually channels gigantic magic to transform and defeat a powerful dark being known as Leviathan. Despite his brutish and single-minded nature, he is not depicted as a malicious person; he simply possesses a very strong and uncomplicated personality that clashes frequently with the fantasy world he despises.