Akira Nishio is a second-generation Fafner pilot from Tatsumiyajima Island. The deaths of his parents in an early Festum attack rendered him mute by trauma during the original series, appearing in shelter scenes and classroom settings without dialogue. Following Soushi Minashiro's return, Akira becomes an active Mark Zehn pilot specializing in long-range combat with the sniper weapon "Dragon Tooth." He frequently serves in expeditionary forces away from the island, operating his Fafner in its original Nothung Model configuration. Akira also co-pilots the massive Zero Fafner, initially intended for his parents, with his twin sister Rina Nishio; this unit was later upgraded with the Canon System to amplify Synaptic Disconnection Phenomenon (SDP) abilities.

During combat, Akira experiences severe assimilation effects, including temporary reddening of his eyes. In one engagement, a Festum penetrates his Mark Zehn's left arm, causing excruciating pain. Soushi Minashiro orders the arm's disconnection when pain-blocking systems fail. Akira subsequently undergoes pulse treatment supervised by Sakura Kaname.

Outside combat, Akira demonstrates camaraderie with fellow pilots. He assists Kazuki Makabe in food preparation at "Rakuen," where his specialty curry earns the designation "Akira Curry." He expresses disappointment when unable to work alongside Maya Toomi and defensively states she lacks a boyfriend during interactions with Human Army personnel. His relationships include protective concern for Maya and close bonds with Hiroto Douma and his sister Rina.

In "Sōkyū no Fafner Behind the Line," Akira is depicted during daily life moments following Soushi Minashiro's return, among characters exploring transitions toward non-combat careers; specific details of Akira's vocational exploration remain unspecified.