His body long and sinuous, covered in dappled brown and black scales, Yai is a snake of ordinary coloration but elegant bearing. He is sleekly muscular, with a somewhat rectangular body, his sides being quite flat. His head is long and smooth, with very flexible jaws, elastic enough to stretch around a large egg. As coloring goes, Yai's scales are predominantly beige, banded with stripes composed of mottled brown and black. The inside of his mouth is shimmery black, and he has no teeth. His underside, lower jaw and the scales edging his upper jaw contrast this, being purely white. His slanted eyes are a pale amber-brown hue, with pitch black pupils that are vaguely slit-shaped.
Yai is acquainted with few and forgotten by many who did not spend much time which him; a rather large number, for there are not many animals that choose to interact with a snake for very long. However, lofty and supercilious, Yai somewhat prefers this. However, he does not like it when animals assume that he is like other snakes. He is usually rude to such animals, though to the accepting he exhibits a certain courtesy most of the time.
While he reclines in a tree, Macheo happens to step upon Yai's scales.