So let me get this straight. The only reference we have for what Himaruya looks like are the drawings he makes of himself?

That and the painting that the royal member from Wy made of him (it’s pretty obvious it’s him, but it hasn’t been directly confirmed).

If you search the “Himaruya” tag on Hetarchive’s English translation of Bamboo Thicket, you’ll see that he’s drawn himself quite a bit. There are also some in a few of the printed volumes.