IF the game company has not given public notice that their assets are free to use for porting to other games, then you would need to have, and submit written proof of authorization by a representative of the company. It would also be good to have a link to their disclaimer, if they have made a public notice of it.
Some games, like Witcher, don't care if you use their stuff. Others do.
Nexus won't support ripped/ported content, if the game company has said that it's not ok. as it falls into the realm of piracy. And they can be sued for it.
Best bet, write the company Koei Tecmo that released the game.
Edit- some companies will let you use their assets for porting, and mods, but under the restriction that it isn't for profit. Meaning that you can't accept tips, or donations, or donation points for the mod, if it's able to be released.
Edited by StormWolf01, 29 October 2019 - 05:18 AM.