Quoted By:
Haatons and it's not even close. No other vtuber pet has featured as prominently on their oshi's content and fan works, no other mascot has had such a consistent design for ages. They were originally created along Akai Haato and then Haachama re-edited them a bit early on and the fans meme'd them until they went mainstream.
They are very recognizable and easy to draw, very cute, pretty much perfect.
Haatons were also among the OG mascots, all other mascots attempt o emulate them to some extent.
Seriously you can't find a better mascot. There from the earliest days, consistent, featured everywhere, recognizable, simple but perfect.