Ikoma began as a steamsmith engineer at Aragane Station, focused on creating weapons to destroy Kabane. He invented the Piercing Gun to penetrate their iron hearts. After testing it successfully during an attack, he suffered a Kabane bite. To prevent full transformation, he restricted blood flow to his brain, becoming a Kabaneri—a hybrid retaining human consciousness with enhanced strength, endurance, and rapid healing. Following Aragane Station's fall, he joined survivors on the armored locomotive Kotetsujo. His hybrid nature provoked distrust from humans, compelling him to repeatedly prove his loyalty through protective actions. He formed a significant bond with fellow Kabaneri Mumei, relating to her struggles. He promised her they would find a way to become fully human again, symbolized by his gift of a green memento stone.

Six months after Kongoukaku, Ikoma arrived in the war-torn region of Unato with the Kotetsujo. He joined an alliance to reclaim Kabane-occupied territory. His analytical skills detected unusual Kabane behavior patterns, suggesting external control. This caused friction with military leaders, leading to his temporary confinement after his Kabaneri bloodlust nearly caused him to attack Mumei. He regained control before harming her, intensifying his internal conflict between humanity and Kabaneri instincts. During the Battle of Unato, Ikoma broke confinement to rescue Mumei from tunnels beneath Unato Castle, saving her from a powerful Kabane variant, a Wazatori. Severely injured, he reaffirmed his promise to her; a mysterious green light healed them both. Inside the castle, he confronted Kageyuki Komai, a former lord turned Kabaneri who created a fused colony using his daughter Miyuki as its core. Ikoma recognized Kageyuki's actions stemmed from grief and a desire to resurrect his daughter, mirroring Ikoma's own fears and motivations. He assisted in defeating Kageyuki and neutralizing the fused colony threat.

After the battle, Ikoma reflected on the hatred spread by Kabane across Unato, deepening his understanding of their nature. His relationship with Mumei progressed significantly; she gifted him a hand-knitted accessory for his stone and kissed him, indicating mutual affection. He consistently demonstrated leadership, technical ingenuity, and a commitment to protecting others, reinforcing his identity as a protector despite the challenges of his hybrid existence.