Reincarnated in Birth Of The Demonic Sword

Mc transmigrates into Birth Of The Demonic Sword and had hundreds of years prep before main events starts. There will be minor multiverse but it is fully explained with reasonable explanation. Also he can only manifest a kind of spirit clone of himself to go to multiverse, his real body can't leave Birth Of The Demonic Sword verse. He only goes multiverse for a chaoter or two so he can get and bring other characters to be with him. Ps this fic is Harem so begone thy Anti-Harem Sect individuals! For I have abandoned the Anti-Harem Sect (ompy this once) so that I may become a true "man of culture"!!!