Small, artificial imitation of Harukana Reine, manufactured by Erina Hikari herself, who was also secretly Iryilicia Syltheril Airya and being an A-takaniai fairy humanoid alien that has lost her wings. Harukana Yui is an artificial body constructed by Airya and her Shingenii collaborators to house her previous ship AI, salvaged in the ruins of the derelicts of her ship.

Once it was reactivated, though before being transferred to her new body, it showed different behaviors than it had shown previously, starting to mistakenly address Reine as mother and to refer to Airya as bigger mama. The AI appears to have lost the memory of what it used to be, however, the instincts of its service with the Phoenix Imperium spatial navy, under A-Takaniai race, are still alive and intact.

Her recent evolution provokes numerous questions related to identity and her essence of artificial intelligence. Though it is made in the spirit of her former predecessor, Harukana Yui has grown into a personal and, actually, surprisingly charming and complicated personality.

Her reflex actions are instinctive indications of a long-standing history with the naval actions she was used to and indicate that although some of this may have been forgotten, some basics of her training seem to survive. As she interacts with her new family Yui changes her behavior to exhibit a kind of innocent curiosity, and a need to connect with reality as she tries to make sense of it.

This process of self-exploration not only puts into question how Yui relates to both Reine and Airya but also provides an opportunity of discovery what she feels like to have a heart, despite being a circuit and code.:::