Missions in Nioh may be undertaken by the player from the overview screen. The following is a list of missions in Nioh along with their rewards. This list will be updated as more information becomes available.
There is a main campaign which you can choose to follow but there are also around 100 side missions where you can take on waves of enemies and get more loot. As for the length of the game, it really depends on how often you die. During your first playthrough of the main campaign, on average you can expect around 40 hours.
Twilight Missions are much more difficult versions of the missions in the game, and feature much better rewards.
The rewards for mission completion scale to your level, even as a visitor engaging in Online cooperative play.
Main Missions in Nioh are the primarly Missions that must be completed in order to complete the game. Many of these missions will, once completed, unlock a Twilight Mission version that is much much harder.