Cluster 

The story begins by introducing three sisters on a central "Heavenly" planet. This central planet is surrounded by 12 other planets or "worlds." The three sisters living on the heavenly planet are princesses (of course!). One day, the eldest sister goes on a training expedition, but does not return. The energetic, peppy, stereo-type-heroine youngest sister goes off to rescue her. There the story begins. On her journey, she begins to have perverse dreams about a dark, sinister man with her eldest sister. Out of nowhere, she meets this guy who has a strange, troubled past. He has psycotic phases where he assumes another personality. Sometimes he's nice, and sometimes he gets really evil-looking and tries to seduce her. She soon meets many other odd people on her journey and they travel with her. Her journey and the adventures become the main story. Includes volume 0. Note: After the second volume, Tamayo Akiyama became the sole credited artist.