Some time after Queen Metallia's defeat and the rebirth of the sailor soldiers, a mysterious meteor landed on Earth, carrying with it two aliens... a boy named Ail and a girl named Ann.

The next day, Usagi had two new school mates, a guy called Seijuurou Ginga and a girl called Natsumi Ginga. 

These two aliens collected energy for the Makaiju (the Doom Tree) which gave them life.  They were very happy for a while on their home planets until, the people started to fight over Makaiju's power.  They became full of hatred and eventually destroyed their planet with all the fighting. The Makaiju escaped into outer space with the remaining creatures, who still continued to fight. The Makaiju became weaker and weaker since it was unloved.

The Makaiju hoped that they would turn out differently. In order to support Ail and Ann's life, the Makaiju put itself to sleep so that it's remaining energy would be channeled to Ail and Ann's growth and development.

But Ail and Ann did not know how to show love for the Makaiju, rather they thought only of stealing energy from others to preserve its life...