Kōta Koga is the younger twin brother to Rakuta Koga. He acts impulsively and with a hot temper, a stark contrast to Rakuta's calm and calculating nature. This tendency toward rash action often leads Kōta to act before thinking things through.

Kōta nurses a clear crush on Yae Yatomi (Yaya). He frequently observes Yaya showing affection toward Hyuuga Mayuki, fueling Kōta's envy of Mayuki and adding tension to their interactions.

His impulsive decisions drive key plot points, notably the Tokyo Tower incident. Eager to impress, Kōta entered a restricted area to replace Minori Izumi's broken souvenir. This reckless act trapped him, Mayuki, Mayuki's dog Maru, and others inside the unstable structure. During the crisis, Kōta worked alongside Mayuki to restore power to an elevator, successfully rescuing Rakuta and Minori, demonstrating his ability to cooperate effectively under pressure despite his usual recklessness.