Help me find

I've been trying since yesterday to find this manga but i couldn't find it.. i don't remember much but i think it was a onshot(full mrm vibes) where the mc is researching something on a cliff i think and he falls inside through some crack ig and then there he gets fucked and impregnated by a monster (the monster didn't had any intelligence).. it had some violent scenes too because the monster don't know how to control his strength and i think he also breaks MCs leg.. we also see their children in the story.... So if somebody has any idea about this one pleaseeee let me knoww!!!!