Every 7 years or so, the planet Earth is subject to a phenomena known as “nova bombardment”, where it is blasted with stellar radiation. The Earth’s geomagnetic field and atmosphere prevent any catastrophic damage, but it does have one major effect. Every so often, an individual subjected to this bombardment mutates, gaining what scientists call a “metagene” that gives them extraordinary powers. These beings are called Novas.
Novas rarely exhibit the same power twice, though slight variations on the same theme tend to be relatively common. For example, the Novas known as “Tag” and “Silhouette” both possess the ability to become two-dimensional shapes, but in Silhouette’s case, she acts as a shadow, and cannot pass through other shadows. Tag, on the other hand, masquerades as graffiti, and has no problem passing through shadows.
These Novas are still human, and can reproduce with humans. Half-Novas can inherit a portion of their parent’s powers, though it is never as powerful as a full-blooded Nova. Any further dilution tends to eliminate the metagene entirely.