Mermaid, Thetis

人魚姫のテティス

A devoted servant of Poseidon, bound to him by a life debt. Thetis was rescued by Julian Solo when he was a young boy; at the time, she was a beautiful fish stranded on the beach, but Julian threw her back into the sea.
During Poseidon's abduction of Athena, she acted as a mediator between Poseidon and Athena's factions. She could not aid her fellow Mariners because she had been defeated by Ophiuchus Shaina. The Saint spared her, and she rescued Julian Solo from the collapse of the Underwater Sanctuary after Athena removed Poseidon's soul from him. Thetis transformed back into a fish as she died, and Julian, upon finding the fish, released her back into the ocean, finally allowing her to rest.