While exploring Tenryu River in Nioh 3, players will eventually run into a locked door in the village area that refuses to open. Unlike most doors in the game, this one cannot be unlocked from the other side.
To open it, players need a specific item: the Dirty Key.
This guide breaks down exactly where to find the Dirty Key in Nioh 3, how to defeat the enemy that drops it, and what players can expect to find behind the door.
Where to Find the Dirty Key in Tenryu River
The Dirty Key is dropped by a Yamainu Yokai in the central section of Tenryu River.
Players will encounter this enemy after the fight with Yamagata Masakage, so it is not something that appears right at the start of the area. The Yamainu is also much more dangerous than it looks, mainly because it does not show a traditional health bar.
Even without the health bar, it hits hard and moves fast, so players should treat it like a mini-boss encounter.
How to Beat the Yamainu
The Yamainu fight is all about staying controlled. Players who try to rush it down usually get punished.
A few things help a lot here:
Manage Ki carefully. Getting caught with no Ki is one of the fastest ways to lose this fight.
Play for safe openings. Wait for the Yamainu to finish its combo, then punish with one or two hits.
Do not get greedy. Long attack strings are risky since the Yamainu recovers quickly.
Use healing smartly. If an Elixir is needed, create space first using the nearby village layout.
If the Yamainu is too strong, it is completely fine to leave and come back later after leveling up or upgrading gear. The locked door is not required for story progress.
Nioh 3 Guide: How to Unlock the Door in Tenryu River
How to Open the Locked Door in Tenryu River
Once the Yamainu is defeated, it will drop the Dirty Key automatically. Players do not need to interact with anything special to pick it up.
After that, return to the locked door in the Tenryu River village area and interact with it. The Dirty Key unlocks it instantly.
What’s Behind the Door?
The room behind the locked door contains a small stash of useful loot, including:
Healing supplies like Elixirs
Crafting materials for upgrades
Amrita items for leveling
A few equipment drops
Nothing here is mandatory, but it is absolutely worth grabbing, especially for players who want extra resources before pushing deeper into Tenryu River.
If players are stuck on this door in Nioh 3, the solution is simple: defeat the Yamainu Yokai and collect the Dirty Key. There is no alternate route, and the door cannot be opened from the opposite side.
It is one of the more straightforward “key item” secrets in the game, as long as players know where to look.