I'll admit, I didn't enjoy Yay as a character initially, but I'm warming up to them.
I like that they are basically a teen in terms of emotions and human (or what-have-you) interactions, and worse - they seem aware of it but can't do much about it.
Also, their hurt expression is adorable and priceless.
One thing I don't like is that they had a much more androgynous look in the beginning, I would say. Maybe it was the way they dressed, maybe something about the way they were drawn, maybe the hair? But they read as vaguely masculine to me, at least to an extent, whereas now I completely don't have that vibe.