Kōga Tsukishima hails from the easternmost island nation called the Land of Vajra. As the eldest son of a prosperous kimono fabric merchant, his existence began under traumatic circumstances: conceived days after bandits assaulted his mother during an attack. This event triggered severe mental deterioration in his mother. His father, consumed by doubt over Kōga’s paternity, descended into paranoia and hostility, treating him as a stranger. Though spared physical abuse, Kōga endured neglect as his father delegated care to servants. Raised for six years in this environment, he grew starved for affection, constantly seeking validation through kindness while masking deep insecurities behind a smile.

His family’s rejection ultimately left him homeless, and he was later sold into slavery under a man named Miguel.

Kōga wields multiple combat abilities, including a Slash Attack, Haste, and the secret swordsmanship technique Tsubame Gaeshi. He also employs Crazy Cherry Blossoms and Iai Flash. His skill Calm and Serene heightens his other senses when his eyes are closed, indicating developed swordsmanship proficiency.

His first encounter with Noel Stollen saw Kōga mistake Noel for a girl. Upon realizing his error and taking offense at Noel’s belittling remarks, Kōga initiated a physical confrontation. This clash led to Noel recruiting him into his clan.

Physically, Kōga is an adult male with black eyes and shoulder-length black hair. He typically wears a scarf and armor. His personality reflects his traumatic past, marked by a profound need for belonging and validation, yet capable of aggression when provoked, as shown in his reaction to Noel.