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 M key here.
Omori Location Key N
You can find the Omori N Key in the casino (Last Resort).
Only Omori can collect the N Key. In case Kel, Hero or Aubrey are leading the party the N letter key will be semi-transparent. A semi-transparent key can not be collected.

Looking for Key O. Find the Omori Key O.
You can find all Omori key locations here.