She is described as childish by Kaguya. It's apparent that she's naive, even sending a jellyfish messenger to the burning desert of Al'Sahra. She's head-over-fins in love with Loue who had rescued her before. She acts jealous towards Liddell as the former believes Loue belongs to her.
One thousand years ago, Oceria was originally a surface kingdom but sank beneath the waves when the Eld Witch's third daughter grew jealous of the kingdom's magic.
In order to get Oceria to fight in the war against the Eld Witch, Alice turned the once human Aquell into her current mermaid form.
She was swallowed by her servant, the Octopus in a Jar (who was apparently a huge 'fan' of the princess), but surprisingly wasn't truly harmed. She gives Liddel her sigil and the Supra Abyss rune. Aquell also opens the door to Al'Sahra to let Liddell check in with a messenger she sent to that kingdom.
In the end of the second playthrough, Liddell meets Aquell and the other princesses at a tea party in Lenore. They tell her that this was all a dream and hope to meet Liddell in the real world and bid her farewell.
Aquell, like Alice and the other princesses, is possibly immortal as she has lived for over one thousand years but has remained physically and mentally a teenage girl. As a mermaid, Aquell can breathe and speak perfectly well underwater as well as above water. Her mermaid fin allows her to swim as fast as a fish.
Aquell's magic is connected to water and she owns the Supra Abyss rune. Aquell's doll can cast a powerful supra spell that summons a water spout.
- Aquell is based on Hans Christian Andersen's fairy tale The Little Mermaid.
- Unlike the Little Mermaid who was born a mermaid and became human, Aquell was born a human but was transformed into a mermaid.
- The fact she fell in love with Lou after he rescued her is ironic as the original Little Mermaid fell in love with the prince she rescued from drowning.
- Her hostility to anyone who could be a rival for Lou's affection is similar to the mermaids from Disney's Peter Pan.
- Aquell and Rapunzel are the only princesses who are not human.