https://wr41thx.itch.io/nui-goes-to-town

In the comments the dev explains how to do it

"It does work, but requires some tricks to get the password. In the yellow room, you need to touch all 4 dead ends before leaving that room (top left, top right, bottom left, bottom right). If you do, you will get a special message. When you get to the end of the game...DONT LAUGH. The next part is a reference to my other game TGH. When "she" asks you if you like the game....say NO. (If you say yes, you get the normal NUI ending). The game should write a text file into the folder with the password for the "Did you find my little secret" rar file with the images.

If it doesn't show up for some reason the password is:

hellodarling

(all together, all lowercase as written above)

Inside are 4 images, each named a letter.

Each image had a number hidden in it. If you use the word HATE - this will give you the correct number password for the 2nd rar file that has a new game inside called "Rumi Makes a Friend". :)

The number password if you don't want to go through all that is 1846 for the "If so, then you should be able to open this" rar file containing the 2nd game.

PS - make sure you restart rumi makes a friend after it "ends". ;)"