Rakuta Koga, the older twin brother of Kota Koga, attends school alongside the protagonist Mayuki Hyuuga as part of his friend group. Rakuta exhibits a consistently calm, pragmatic, and calculating personality, maintaining composure where his younger twin Kota displays impulsiveness and a hot-headed nature. He possesses the ability to predict near-future events, though the mechanics remain undefined.

The twins share a close bond, frequently appearing together at school and during investigations of Kyuto's supernatural occurrences. Rakuta occasionally devises strategies, such as suggesting a plan that led Kota to declare his intent to enter a restricted zone to retrieve a souvenir for their classmate Minori. This decision prompted both twins to join Mayuki and others exploring the abandoned Tokyo Tower.

Rakuta wears the standard school uniform complete with tie and crest. He has distinctive white hair styled to his ears and blue eyes. His role within the group is supportive, contributing to the character dynamics during their adventures.