If 3D is PD, what is 4D?
Don't you mean, when is 4D?
I dunno, go ask the 5D otakus who jerk off to them.
The Touhou character Sakuya can operate a fourth dimension, so she is 4D, we just interpret her as a 2D character. With every dimension, more flaws appear, so she must be fairly horrid to look at.
Isn't the fourth dimension time? It probably means moving objects then.