Early in your adventure through the Blighted Lands, you may discover a big mysterious door that will need a Red Key before it can be unlocked. You’re unlikely to have the Red Key in your possession when you find the door, so don’t worry about it yet, but you will have it in your inventory before the end of Chapter 1.
So, work through the campaign until you get to Subcity 03; this is when the path to the Red Key and the door it unlocks becomes clear. The Red Key actually unlocks two different doors, so here’s what you need to do to find the Red Key in Beast of Reincarnation – and the mysteries it unlocks behind each door.
Where to find the Red Key

As you’re progressing through the campaign in Chapter 1, you’ll be able to find the Red Key within Subcity 03 during the main quest, Toward The Nushi’s Lair. The entrance is located near where you fought the Rangifer Nushi boss on the northern part of the lake.
The first battle with the boss will need to be completed before you can enter Subcity 3, so make sure you’ve completed this. If you haven’t learned how to parry yet, now is the time.
Once the boss is defeated, Emma will be thrown into a flashback sequence where you’ll need to seek out the Malefacts until the sequence is over. Once it is, Emma will wake up back in the Cleanse Walker. Heal and tool up, and make your way to the entrance of Subcity 3.
Turn the large crank to open the entrance and head inside. While exploring Subcity 03, you’ll come across a big ornate bronze door and a Retired Gatekeeper Golem nearby. Unlike many of the other Golems, this one is friendly and will give you the Red Key after a conversation during a cutscene.
Of course, this is just one of three keys you’ll need to find, as you’ll also need to hunt down the Blue Key and the Yellow Key, but the good news is these are quite easy to find.
With all 3 keys in hand, you can progress the story and go through the big mysterious door. However, the Red Key also unlocks the wooden door inside the Abandoned Village.
Unlocking the door in the Abandoned Village

Once you have the Red Key, you can retrace your steps back to the Abandoned Village from near the start of the game. Here, there was another locked door, not quite as grand as the one in Subcity 3, but the Red Key also works on this lock.
Use the key, and you’ll be able to enter and find a Strongbox that contains 558x Amber and an Ancient Book. You can never have too much Amber, and the Ancient Book will be useful later in the game.
Now that you’ve looted the Strongbox and have the Red Key, you can begin the hunt for the Blue and Yellow Keys to open the big door and progress to the end of Chapter 1.

