In the beginning of time, well, we don't know what happenned then, but somewhere along those lines the dimension of Hutangwee was born. In order to understand where Groovin' comes from you need a basic understanding of Hutangwee, our dimension, the dimension in which humanoids are the sentient beings of their realities.

Hutangwee is built of several different parts. It has three corners, these are the anchor realities: Gaia, Galthasar & Planet Wasteland. We, of course, are familiar with Gaia, our home reality. Galthasar is a fantasy world filled with goblins, faeries & magic and the like. Planet Wasteland is a savage reality filled with technology.
Now, in the middle of these corner, primer realities is Limbo, home of infantile realities trying to grow and become stable enough to create a new corner. When a reality breaches through Limbo it becomes a pocket reality while it grows in size and strength. However, any reality can be engulfed by another larger reality in an osmossis style.

There is a lot more to Hutangwee, but for the sake of explaining Groovin' this is all you need to know. Groovin' is a pocket reality that was simultaneously attemptedly attacked by Gaia & Galthasar. This attempt failed for corner realities repulse each other and when the two tore away from Groovin' they each left a small part of themselves attached.