The Tailwater Key is a step on the way to the Yellow Key, one of three keys Emma and Koo need to reach Nushi’s Lair in Chapter 1 of Beast of Reincarnation. Unlike the Red Key and Blue Key, the Yellow Key is locked behind an extra step. You have to find a hidden cave, clear a mini-boss, and only then can you open the door that leads to it.
Quick answer: Go to Tailwater Village in the Ogouchi Buffer Zone, enter the cave at the village’s northern edge, and defeat the Grizzly Malefact mini-boss. It drops the Tailwater Key when it falls.

Where to find the Tailwater Key cave
The key sits inside a cave that is easy to walk past. Head to Tailwater Village, which is part of the Ogouchi Buffer Zone. From there, make your way toward the northern edge of the village. A cave entrance is tucked into that side of the map, and the Grizzly Malefact is waiting inside.
| Detail | Info |
|---|---|
| Region | Ogouchi Buffer Zone |
| Location | Tailwater Village, northern edge |
| Guard | Grizzly Malefact (Level 10 mini-boss) |
| Reward | Tailwater Key |
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The Grizzly Malefact is only a mini-boss, but it shows up early, so your skills and gear are still thin. Unlocking a few useful skills before the fight makes it noticeably smoother. The Roll skill in particular is worth having.

When the Grizzly Malefact goes down, the Tailwater Key drops as your reward. You will see it added to your inventory, confirming the fight is done.
How to turn the Tailwater Key into the Yellow Key
Holding the Tailwater Key is not the end goal. It exists to unlock the door that hides the Yellow Key, so stay in the cave after the fight.
With the Yellow Key in hand, you have cleared the trickiest of the three keys. Pair it with the Red Key and Blue Key to open the path to Nushi’s Lair and keep pushing through Chapter 1.






