Akira Miyamoto is the younger brother of Atsushi Miyamoto. Following Atsushi's unexplained two-year disappearance, their family fractured, with parents frequently comparing Akira to his missing brother. Their father, Seika Miyamoto, previously worked at a shop before the family's decline. Akira faced personal turmoil, including his childhood crush Yuki Sakashita dating his best friend Ken Saito.

Akira's life shifted dramatically when he discovered an unconscious woman, Rei Aoyama, near his home. Rei revealed Atsushi was alive but imprisoned on Higanjima Island, overrun by vampires. She initially presented Atsushi's ID as proof, but later confessed her true purpose: luring victims to the island under vampire coercion to protect her own family.

Determined to rescue Atsushi, Akira organized a trip with friends under the pretense of a graduation celebration. Vampires attacked their boat upon arrival, capturing everyone except Rei. Akira and his friends narrowly escaped initial capture. On Higanjima, Akira finally reunited with Atsushi, who explained the vampires' origins and their leader, Miyabi. Atsushi admitted to freeing Miyabi, causing the island's downfall and leading to Miyabi murdering his fiancée Ryoko.

Akira trained under Atsushi to fight vampires, later receiving advanced instruction from Atsushi's master, a mutated oni resistant to Miyabi's control. This training honed Akira into a capable fighter. After Atsushi and Rei perished, Akira assumed command of the human resistance against Miyabi.

Confronting the vampire virus's spread to mainland Japan, Akira continued leading survivors against Miyabi's forces. He focused on protecting friends and stopping the vampire invasion despite repeated setbacks, including failed escape attempts from the island. Haunted by feelings of inadequacy in protecting allies, Akira relentlessly pursued greater strength through rigorous training. His resolve remained fixed on defeating Miyabi and saving humanity from extinction.