It's a straight r18 manhwa, I think the girl is supposed to deliver something for the elderly in the village but she walks on that elder's grandson fully erect.
The Obsessed Mage and His Beloved Statue Bride - Crane
definitely not
I assumed...
I've lost hope finding it, I used most AIs.
Anyway, the plot is a girl comes back to her hometown and she runs an errand to give something to an elderly but she stumbled upon the grandson of that elderly. BUT the grandson was pleasuring his big tasty looking cock with that damn toji build physique. I skipped it since I know I'll get so horny if I read more and forgot to bookmark the name. But damn dick so good it lasts in my mind for years now.
I think it's r18 hentai manhwa? thank you fellow perverts