Amphitrite is a Nereid. She is a mermaid with a pale orange mermaid tail and fins and turquoise hair decorated with seashells. Poseidon is Amphitrite's Husband. She becomes an MOA student after helping save the world from a group of titan giants. She can shapeshift from having a tail to having legs. She possesses a magic pearl that she wears as a necklace. It protects her from land sickness so that she can stay on land as long as she wants. Her roommate is Calliope.
It is revealed that she has 49 sisters and her and her twin Thetis is the oldest. Because she is a Nereid, which is a type of nymph, she is neither mortal nor immortal, but is somewhere in between. Because of this, she can use winged sandals, but like Echo, can not fly that high up with them.