Ail and An are aliens from another planet, searching for energy to keep their tree alive. They arrived in Tokyo one evening as a big bang, leaving a crator in the middle of the city. Ail and An brought their tree with them, known as 'The Tree of Life'. The tree is what sustained their race. Little did they know at the time, that the tree needed positive energy, not the negative energy that they had been giving it. So, in order to collect energy, Ail and An assumed human form, taking the names Seijuurou (Ail) and Natsumi (An). They enroll in the local junior high with Usagi and gang. All the girls love Ail. An has a rather nasty attitude. Ail falls for Usagi and An falls for Mamoru. Although, otherwise, the two seem to be lovers. Ail carries around a flute with him, with which he calls forth Cardians. Who in turn go get energy for them. Ail and An were turned to the good side, when Sailormoon made them see how wonderful it is to love and find goodness.
