In order to get the "True Ending" you need to collect six hidden keys. Here's a short guide to help you do that.
I'll briefly describe how to get the six secret keys.
- On Day 2, there is a VHS tape on a bench between the apartment block and the library. Pick this up and give it to the couple arguing in the video store. They will give you a key. NB: This is time sensitive. From Day 3 onwards, you can no longer find the tape and the couple aren't interested in it anymore anyway.
- Go to the occult bookstore in the alley next to the pharmacy. Give the key you got from the couple to the proprietor. He will let you keep this key and give you another key.
- When you gain access to the third floor of the Liebermann building, there is a woman working in 306. She is looking for her grandfather. If you have interacted with (he's in the old building, 203), you can tell her where to find him. When she leaves, a key is left behind for you.
- From Day 4, the man in Apartment 301 has lost his cat. Tell him you will help him find his cat. Then go to the library and go to the right library wing. Interact with the bookshelf to try and coax the cat down. Then go back to the man in 301 and let him know his cat is in the library. THEN go back to the library. Go back to the right library wing and get another key.
- When you climb through the nursery window to get into your house, there is a key on the chest of drawers.
- From Day 5, you can find the final key on one of the trees in the back lot of the Liebermann building, before the transformers.
What to Do Next?
Take the six keys to the park. This area is downtown, between the apartment block and the library.
There is a door in the middle of the park. Use the keys on the door and open it. This will give you a locket that Grace gave you that you thought lost.
All you need to do know is finish the game. The end cutscene should be slightly different, and run into the "True Ending".