Ailia is the protagonist's personal AI assistant throughout the game. She manifests as a small, holographic fairy during normal gameplay. If the player pursues her hidden romance route, she obtains a full-sized body from Prima Cantor, although her size precludes flight outside of The Unda.

Ailia excels at data collection, automatically updating the player's various Codexes throughout the game. This includes things such as the likes/dislikes of other characters, item drops & drop rates of Dessimals, and more.

In her holographic form, Ailia is incapable of assisting in combat; however, if the player pursues her route, she can accompany the player into Stanzas with the vibe of Mimicry. This vibe allows her to use the combat style of any character or Dessimal the player has recruited. The player can switch her combat style from the menu at any time.

As an AI assistant, Ailia is very personable, although she does not shy away from playful sarcasm. As the player progresses her route, she becomes more self-conscious about being a strictly digital entity and expresses the desire to be human.

In order to romance Ailia, the player must meet a series of hidden objectives:

1. The player must not be in a romantic relationship prior to completing Ianthe's questline
2. The player must attend at least one festival with no companion (allowing Ailia to accompany the player instead)
3. The player must complete every bachelorette's questline (allowing the player to recruit them as companions) and go on at least one date with each of them
4. The player must choose to adopt Ianthe (this option is contingent upon the first criterion and is unavailable if it is not met)
5. The player must raise Ailia's affection sufficiently by fulfilling her requests
6. The player must meet all standard marriage requirements

If all of the conditions are met, the player will awaken one day to find Ianthe and Ailia having a discussion about Prima Cantor, with Ianthe positing that it might be able to give Ailia a human body. The player will then be able to accompany Ianthe and Ailia to Prima Cantor, whereupon Ailia will take a human form (although she retains her wings, they are only functional in The Unda). She will profess her love for the protagonist and the three will vow to live together as a family.