Akina Nanamura, Kazuto Tokino's neighbor and childhood friend, wields significant spiritual powers like demon wards and defensive barriers. After Princess Hydra of Valhalla crash-landed on her family shrine, causing destruction, Akina punished her by sealing away her powers, transforming Hydra into a child-like form. Hydra stayed with Akina to work off the damages from the crash.

Akina harbors unspoken romantic feelings for Kazuto, often visiting his bathhouse without confessing. She later confronts the reality of Kazuto and Valkyrie's love and impending marriage, leading to regret over her inaction. Hydra frequently mocks Akina's self-consciousness about her breast size. In the second season, Valkyrie temporarily enlarges Akina's breasts using the Key of Time at Hydra's joking request—a change Akina enjoys until Valkyrie reverses the effect.

Her relationship with Hydra is volatile, filled with arguments and physical fights, often sparked by Hydra's taunts about Akina's appearance. Despite their animosity, intense disagreements trigger their fusion into a powerful warrior named Akidra, combining their abilities and enabling internal communication. This fusion reverses if they become too agreeable. Akina is also a notoriously terrible karaoke singer and allergic to cats; Hydra once comforted her during an allergic distress. Valkyrie's time magic also temporarily regressed Akina to a child, a state Hydra worsened. During the second season's conflict with Valkyrie Ghost, Akina discovered and utilized her fusion ability with Hydra to confront the threat.