As it says , i'm looking for something similar to https://www.novelupdates.com/series/let-go-of-that-primordial-man/ & https://www.novelupdates.com/series/i-have-a-mansion-in-the-post-apocalyptic-world/ and maybe a bit of https://www.novelupdates.com/series/mechanical-god-emperor/ Basically, something where the MC is the only one who can travel freely to one or more world, bringing technology or resources inbetween them, strengthening his foothold and powerbase in both (or more) worlds I'll accept both novels which have lots of translated chapters already and novels which don't have a lot or none at all, but in the latter cases you'll have to provide synopsis, the name and a possible site where I could find it R-18 is no issue Considering the situation, them not having harems is near impossible, so that's okay too Male MCs only ( some chapters from female sidecharacters is okay, but MC has to be male)
Try "The Empress's Gigolo"? Might be a good fit. MC is teleported back and forth between two worlds. One modern world the other a primitive cultivation fantasy world. Spoiler He doesn't have control of teleportation in the beginning. Things change a bit as he cultivates. It's kinda slow at times.
I felt like it gets better on. Start is really slow. When the empress acknowledges him it starts to pick up.