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 L key here.
Omori Location Key M
You can find the Omori M Key in the bottom of the well before entering the Last Resort.
Looking for Key N. Find the Omori Key N.
You can find all Omori key locations here.