Kōichirō Ōta, known as "Coach," survived the 2015 Luxion fleet disaster where alien forces attacked deep space explorers. Captain Yuzo Takaya sacrificed himself during this event to secure Ōta a place on an escape shuttle. This act left Ōta with permanent injuries: blindness in his right eye and leg damage requiring a mobility cane. He consistently wears aviator sunglasses to conceal the scar over his injured eye.

He serves as the Machine Weapon coach at Okinawa Girls' Space Pilot High School and leads the Gunbuster development program. Driven by a debt of honor to Captain Takaya, Ōta selects Takaya's daughter, Noriko, for the elite Top Squadron despite her inexperience and others' skepticism. He drills her relentlessly to unlock her pilot potential, emphasizing discipline and perseverance.

During the Top Squadron's operations, Ōta contracts Space Radiation Sickness. His condition becomes critical in a pivotal battle against space monsters, leaving Noriko and Kazumi uncertain of his survival. They fight in his memory, with Noriko declaring the Gunbuster embodies "Coach's heart." After this battle, Ōta and Kazumi reconcile their mutual feelings and marry.

Ōta dies in the 15-year interval between the space monsters' defeat and the completion of Buster Machine 3. Supplementary materials indicate he survived approximately 12,000 years beyond the main events, attributed symbolically to "Hard Work and Guts."

His character design features long dark green hair and green eyes. The cane he uses pays homage to Dan Moroboshi from the *Ultraman Leo* series. He is loosely inspired by Jun Munakata from *Aim for the Ace!*, and his name references manga artist Nao Minda, whose real name was Kōichirō Ōta.