There are no harem in nano? He got one girl only. I can't say for the novel but st least in the comic he only got one girl. Thee is one other who is kinda into him but its not a big part, like two panels or so, and he is not into her.
He stuck to one girl in the novel as well!
Spoilers for Nanomachine/DotDG
It is a harem... We already saw him have sex with Yogun (white haired girl) in the manhwa, which is probably where they dropped it off and yeah, it wasn't a panel or so.
Later on Yeo Woon marries her, continues to have sexual relations with her and ultimately have a child together.
There is also another woman in the sequel, though not officially his wife, the cult views her as such because of how close they are.
So dropping it because of harem is valid since it is one.
i rlly hope this has no harem bcs i love the fl i loved nano machine sm but dropped it the moment the author made it harem