Nioh is a Dark Souls-style game through-and-through. It might not be an identical twin, but the DNA is impossible to miss, right down to the way cooperative play is handled. That changed from the demo to the official release, though, and some fans are not thrilled about it.
In the pre-release version of the game, you could join your friends in battle by using a shared password, experiencing the game as a cooperative pair, exploring each new area fresh. In the retail version, things are a bit more Souls-like. To summon another player into your world, they have to have already beaten the area you’re playing. This is intended to make the cooperative experience more organic and the experience a tougher one, but it’s left fans who’d planned on playing the game together feeling disappointed.
Article source: https://www.technobuffalo.com/2017/02/09/nioh-co-op-changed-in-the-final-game-and-fans-are-not-happy-dev-responds/