Miki Naoki is a Chrysalis agent who works for the Shoshidai, an organization dedicated to collecting and containing cursed weapons. He is an anime-original character whose past is not clearly detailed, but he has some prior history with the Shoshidai and came into possession of the Fallgon Sword, a cursed weapon that grants him power. Physically, he has short brown hair and brown eyes, and he dresses in a range of outfits including a leather jacket and shirt, suits, and tactical gear depending on the mission.

As a Chrysalis, Miki wields the Fallgon Sword and is sent on dangerous assignments to retrieve other cursed artifacts. He is portrayed as a reliable operative who takes his duties seriously, though his personality is not extensively developed. He forms a close bond with Marcus, whom he considers a friend, and he is also involved in a secret romantic relationship with Mina Hiraya, keeping their connection hidden from their fellow team members.

In the story, Miki appears primarily as a supporting figure who assists in key missions, such as when he acquires the Azoth Sword and is ambushed by Marcus and Miura, or when he later escorts Marcus to Shoshidai headquarters. He also participates in covert operations, such as an infiltration to retrieve a legendary halberd. His role is that of a dedicated field agent who works alongside the main protagonists, though his individual character arc remains limited. His abilities stem from being a Chrysalis, allowing him to wield the cursed Fallgon Sword and engage in combat against monstrous Busoma, but specific feats or unique powers are not emphasized. Over the course of the series, he remains a steady presence within the Shoshidai, contributing to the organization's efforts without undergoing significant personal transformation.