nioh graves

    There is a hard 5 minute cooldown on downloading grave data. There is no way to get around this limitation in-game. Switching from mission to mission quickly will cause no graves to be loaded in the mission.
    You can however, get around the cooldown by restarting the game completely. IE: go to a shrine to force a save, then close the application and start it again.
    If you start a mission and are on cooldown, the game will automatically attempt to download graves once the cooldown is up.
    Interacting with a shrine or dying will cause the game to attempt to download grave data. Unlike starting a mission however, this won't be queued to do so once it can.
    You can safely interact with a shrine over and over to try and get the game to download new grave data, it won't affect the cooldown unless it actually can download new grave data.
    Every mission has its own grave list, including difficulty. IE: Isle of Demons and the NG+ Isle of Demons have their own grave lists.
    Each mission has a limit to the number of graves it will show for the entire mission. It will populate the level with a limited number of graves closest to the last shrine you interacted with, or near the start of the mission when first starting it.
    Since there is a limit to the number of graves in an area, new graves created by players dying push old graves out of availability. I personally call this "cycling" but there's probably a better word for it.
    The more frequently players die in a level, the faster older graves become unavailable.
    You generally only need to die once to create a grave.
    After you die, it can be a minimum of several minutes for it to appear for others. This seems to be affected by region and activity-- on the weekends it has taken over 30 minutes for a grave to show up.
    A player can have one grave per mission. I don't think there's a limit to the number of missions one can have a grave in, but that's untested.
    You can kill the revenant from the exact same player grave as many times as you'd like, so long as you can get it to show up.
    Developer revenants have a red name and will not have a date/time.
    Developer revenants will not show up again when killed until the mission is restarted completely.
    There is no limit to how old a player grave can be for it to show up, so long as it hasn't been cycled out.
    Gear a revenant drops will drop as the original version of the item before any refashioning/reforging/inheriting applied.
    Gear will drop at the level the revenant has it at, but without any plus level attached. IE 150+10 will appear as 150.
    Gear that is past level 150 will drop at level 150. IE 320 will appear as 150.
    Gear that developer revenants have equipped have random rarities, determined on mission start.
    There are developer revenants who have unique gear not found anywhere else.
    There is a bug in some cases where gear won't have any effects attached aside from its set and fixed effects.