Did a Sona/OC vs IRL Species thing on the Twitters and this is what San is supposed to be. A Llama. I know. Hero Forge has many limits so that's what I went with, but he's supposed to be a llama.

A lot of people in the fandom (Almost all 10 of us) think he's an alpaca and the wiki says that, but given he appeared so little and there is little chance anyone is really going to give an official answer, I headcanon my OC version as a woolly llama. My reasoning is he's taller than most alpacas seen in the manga, his wool is coarser looking and shaggy, and his ears were more banana-shaped. So he's a llama. Fight me... no really, square up!