Aqua Marine is a selkie who lives at Mermaid Lake together with different types of mermaids, like mermaids, sirens, rusalkas, other selkies and more. She is loyal in front of Undine. She is a good person with a nice singing voice and even loves to sing in duets. Aqua can also change the form of her lower body between human legs for walking on land and seal tail for swimming in the water. In humanoid form turns the seal tail together with the fur into a skirt. By using her club and danmakus she also knows how to fight and hunt or protecting Mermaid Lake if necessary. In general she is a loyal, lovely and a kind hearted person.
Mermaid Lake is a place that can be found in a kind of a second Gensokyo that was once a part of the other Gensokyo.