You didn't even know what animal Nezu was. A bear? A cat? Or a mouse? No idea. It could be all of the above, it could be none. The possibilities and your imagination were endless, this increases when you ask him about it.

In fact, one day you were going to ask his office, but instead of finding a huggable mouse/bear/cat you found an equally huggable white-haired boy.

That was the day you discovered that Nezu can transform into a human.