In the Omori game you can obtain a number of keys. These keyboard keys are labeled with a capital letter. The letter keys start with A all the way to Z. You can find the U key here.
Omori Location Key V
As you’re headed to the green puzzle, you’ll see the V key in a cage that only Aubrey can break. Switch back to Omori to pick up the key.

Looking for Key W. Find the Omori Key W.