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 T
You can obtain the T key by doing a challenge or a time wait. For the challenge (Experiment 667) you need to hit the bubbly tank with Aubrey – switch to Omori and get the T Key. For the time wait you need to complete the Humphrey section and Humphrey will spit the T Key out – including you.

Looking for Key S. Find the Omori Key S.