Maeterlinck no Aoi Tori

On a snowy Christmas Eve, Tyltyl and Mytyl sit in their home. Normally, they would be caught up in the Christmas spirit, but their mother has taken ill. So that evening, they lie awake, unable to sleep, when through the window crashes a strange, mercurial magical spirit named Berylune, who reveals that the world we live in isn't the only one there...