Eir Aoi stated “It’s really is an honor for me to be able to sing the theme song again for an anime that was made me so emotionally happy.” She stated that she sang the song to portray “the positive feeling of walking together with an important person [to face] whatever there might be”.

Sword Art Online Extra Edition will be a recap of original Sword Art Online anime and will include new footage. According to the synopsis on the official website:

Kirito and the gang decide to challenge an ALO underwater quest when they learn Yui wishes to see a whale. Finding out that Leafa (aka Suzuha) cannot swim at all, Asuna and the girls to give Suzuha a special swimming training in the real world. On the other hand, Kirito meets face-to-face with a certain person—

Another reason to be joyous during the upcoming winter holidays! Be sure to stay tuned for Eir Aoi’s new song that will be aired during Sword Art Online Extra Edition on New Year's Eve!

SOURCE: リスアニ！