Hydra, one of the eight princesses of the planet Valhalla, serves as a rival to Princess Valkyrie. Unlike Valkyrie, she retains her adult consciousness while transformed into a child form. This state resulted from crash-landing at Akina Nanamura's temple on Earth, where Akina sealed her powers in retaliation for property damage during Hydra's attempt to forcibly return Valkyrie to Valhalla. Akina's will alone can temporarily break this seal, restoring Hydra's adult form, though the process of reverting to childhood lacks full explanation. In adulthood, she wields flight, superhuman strength, energy blasts, and the ability to transform into a winged pink and yellow horse.

Hydra displays a tomboyish, headstrong, and short-tempered personality, frequently acting on impulse without forethought. She originally pursued Valkyrie to Earth to evade a political marriage intended for Valkyrie after her flight. Over time, her priorities shifted, leading her to settle into Earth life. She habitually teases Akina about her breast size, provoking physical retaliation. Despite such clashes, they form a close friendship and cohabitate. Their heated arguments sometimes trigger a fusion into the formidable warrior Akidra, merging their powers; this fusion dissolves if they become excessively agreeable. During her Earth residency, Hydra mastered kendo, leveraging prior sword-fighting training from her academy days with Valkyrie.

Her relationships remain multifaceted: she initially considers Valkyrie a nuisance but evolves a grudging friendship; she befriends Kazuto Tokino platonically; she maintains ordinary camaraderie with Rika Tokino; and she reacts with terror toward Sanada, Valkyrie's maid. Among fellow Valhallan princesses, she voices annoyance toward Laine and Chorus. These evolving connections underscore her integration into Earth society, with her presence continuing into the fourth season, *Banquet of Time, Dreams, and Galaxies*, as part of the ensemble.