|“||"I accept the Laws of the Selector. And now, a new Eternal Girl will be born!"||”|
An Eternal Girl (夢限少女 Mugen shōjo) is a Selector who becomes their ideal self, the person capable of fulfilling their wish. Becoming one is the goal of a Selector.
A Selector becomes an Eternal Girl when certain conditions are fulfilled. The conditions for an Eternal Girl always require that the Selector win a number of battles; the number varies from wish to wish. There can be other conditions required for becoming an Eternal Girl, aside from winning battles. When a Selector fulfills these conditions and is about to win a Selector battle, the LRIG has the Selector recite an oath before both the LRIG and Selector finish off their opponent.
I accept the Laws of the Selector. And now, a new Eternal Girl will be born!
Watashi wa ukeireru sentaku-sha no kotowari o. Soshite ima koko ni, arata no mugen shōjo ga tanjō suru!
However, when this occurs, the Selector does not keep their own body: instead, their LRIG inherits their body, while the Selector becomes a new LRIG. In this way, the Selector becomes the person capable of fulfilling their wish, but in a way unintended by the Selector. The LRIG who inhabits the Selector's body is still obligated to fulfill the Selector's wish, and cannot simply abandon the wish after becoming human. If the LRIG does not attempt to fulfill the Selector's wish, they eventually disappear. For some wishes, the LRIG has to live the wish out rather than just fulfilling it once: for example, in Fumio Futase's case, she has to continually fulfill the original Fumio's wish of becoming a novelist by releasing more novels.
In the event that a LRIG is about to swap bodies with their Selector, and given the Selector was once a LRIG and wishes to be a LRIG again, the LRIG can choose to either take over the body or leave it. If the LRIG chooses to leave the body alone, both the LRIG and her Selector (by this point a LRIG) are sent to Mayu's white room. Since the body would have no soul, the original owner of the body would be forced back to reside in her body, even if they are currently another Selector's LRIG. Such is the case with Iona Urazoe, when Tama refused to take over her body when Ulith was about to become a LRIG again.
LRIGs generally do not reveal the above truth to their Selectors; if they did, and the Selector decided to stop battling as a result, they would forever lose their chance to regain a human body. The Selector would neither win battles, becoming an Eternal Girl and exchanging places with the LRIG, or lose battles, losing their Selector rights and returning the LRIG to the cycle until they appear to another Selector. This is not a hard rule, however. If a Selector does choose to keep battling even though they know the truth, the LRIG can still escape from the card.
As demonstrated in selector infected WIXOSS Episode 12, the oath is required to be repeated in its entirety for the wish to be granted. It is possible for a Selector's wish to interrupt another Selector in the process of becoming an Eternal Girl.
It is also shown (and confirmed in selector spread WIXOSS Episode 1) that a LRIG can refuse to accept their Selector's wish, preventing them from becoming an Eternal Girl. This will usually not happen in most cases, as most LRIGs would want to escape from their card, but in some cases, a Selector's wish might be detrimental to the LRIG. In Tama's case, she did not want Rūko to become a LRIG, separating her from Tama. In Iona's case, she wants to keep battling forever, and Rūko becoming an Eternal Girl would bring an end to her battling.