Osper is the main character of the anime Fight! Osper. He is a young male psychic from the underwater civilization of Mu, a society that came to live beneath the ocean in dome-covered cities after the destruction of its original continent. Over many years, the people of Mu developed paranormal abilities, and Osper grew up in this community as one of its most gifted psychics. He is described as having blue eyes and short blue hair that reaches roughly to his ears.

Osper is defined by a strong sense of justice. He is sincere, determined, and fair-minded, and he tends to act for the sake of protecting others rather than for personal gain. This moral character places him in direct contrast with Drome, an older and more brutish Mu psychic who is vengeful and evil. Each year, Mu holds a tournament to determine its strongest psychic, and Osper battles Drome in this competition and wins. Humiliated by the defeat, Drome destroys the dome of Mu in revenge and escapes to the surface world, Earth. Osper is then sent after him, both to avenge his people and to stop Drome from causing further harm. This mission becomes his central motivation throughout the story.

Once on Earth, Osper meets Yumi Kaizu, the daughter of the chief of the International Crusader Police, a special police force. With Yumi's help and the collaboration of her father's unit, Osper joins the organization and uses it as a base to track Drome. Strange incidents begin occurring on Earth on an unprecedented scale, and Osper discovers that Drome is connected to all of them. Over the course of the story, he confronts Drome repeatedly, solves the cases surrounding these incidents, and forces Drome to flee each time.

The conflict reaches its climax when Drome, cornered, activates an ultimate weapon intended to destroy the Earth and engages Osper in a final battle. Osper emerges victorious, and Drome, in defeat, admits that the evil he committed stemmed from his inability to defeat Osper. Drome then reveals the location of the ultimate weapon, which Osper manages to stop before it can operate, allowing both him and Drome to return to their home beneath the sea.

Osper's key relationships shape the narrative. His rivalry with Drome is the engine of the plot, as the two possess comparable supernatural power and Drome's obsession with Osper drives his destructive behavior. Osper's friendship with Yumi Kaizu is his central bond on Earth. She brings him into the police unit and supports his mission, and their mutual respect is evident in the letter Osper leaves for her upon his departure, in which he writes that the next time they meet he wants to be an ordinary person. This message reflects both the closeness of their connection and Osper's desire for a peaceful and normal life once his duty is complete.

Osper's development across the series moves him from a champion of his underwater home into a protector of Earth. He begins with a mission of justice and vengeance against Drome, grows into a figure who repeatedly safeguards ordinary people from paranormal threats, and closes the story by choosing to set aside his extraordinary role in favor of an ordinary life. His notable ability is his strong psychic power, which is comparable to Drome's and enables him to win Mu's psychic tournament, engage Drome in direct combat, and overcome the final threat to the Earth.