Haidora in the original Japanese, she is a younger sister of Valkyrie, who she chased her to Earth. She knew that if Valkyrie ran away she would have to take her sister's place at the wedding which was not something she wanted to do; however she crash landed on Akina's temple, only to have her powers sealed by Akina making her become a child just like Valkyrie. However unlike Valkyrie her mind is that of her adult form, not a child's. Much like a kiss can restore Valkyrie, the seal on Hydra can be released at Akina's will. Hydra has a short temper and is rather tomboyish acting in a rash manner that shows action before thinking things through meaning she is prone to destroy things that get in her way. She can transform into a winged pink and yellow horse and has several other powers. She has taken up kendo while living with Akina, and often pokes fun at Akina's breast size and her feelings for Kazuto.

When the friendship between Hydra and Akina breaks down, they can combine into a single person, Akidra.