The forms and powers of others Marchens
The appearance of white and black dragons arose with the construction of Reverse London
Dragons are native creatures of this dimension and were like any other creature of a fauna native to somewhere. But with the arrival of humans,some of them started to feed on negative emotions and became monstrous creatures. All marchens have "crowns" or head ornaments
Noel is part-dragon.
- In line with this theory, Noel is only once shown without her horn-shaped hair clip. One would be forgiven for drawing comparisons between this clip and an Arrancar's mask remnants. Her being part Japanese may also factor into this, possibly making her a descendant of an Arrancar or Vizard.
The lack of Hollows is technically thanks to Aizen.
After he exposed Hirako's group to the Hogyoku, and got Urahara and Shihouin banned, either the latter or the Vizards hid in Reverse London, which Wing Bind only allowed so long as they would prevent Hollows from feeding on Witches and Wizards.