Brothers in Human Nature [Not Related by Blood]

The young lord contracts a plague and is abandoned in the deep mountains to be buried.

A snake swallows him and takes human form.

It learns social etiquette, adapts to human life, and hopes to rule the world by reproducing.

It sets its sights on the family's naturally airheaded, useless duke's heir.

The tropes may change.

A few tips for readers:

1. Beastfolk.

2. A gloomy, scheming snake top who has no grasp of humanity × a clumsy, innocent, doting older brother with a cognitive disability bottom. One-on-one romance.

Theme: Build a strong sense of self-worth. Your existence is valuable in and of itself.