Please note: all credit goes to DaftMaFunk!
Guide on how to unlock the secret Monika route. It requires a little file manipulation.
Other DDLC Guides:
Ever noticed how you can’t impress Monika on the poem writing scene?
As you can see, Monika is not visible in the bottom right. But it’s still possible to impress her, though it does involve manipulating files.
Make sure to open the Doki Doki game folder by right clicking the game in your library and selecting properties, then going to local files and clicking browse local files.
Alternatively, you can go into This PC, program filesx86, Steam, Steam apps, common and finding Doki Doki Literature Club in your list of games.
Which Files to Manipulate
First, ensure you are on a fresh install of Doki Doki.
This can be done by uninstalling the game or by deleting a folder in the games directory called ‘first run’. You can find it in the ‘game’ folder.
Next, ensure you boot the game at least once and hit ‘new game’. Ensure you save at least once too.
Finally, you want to go to the ‘characters’ folder and delete every character except Monika.
And That’s It!
You’re done! Just boot up the game and Monika will be the only character in the game, opening up her route.
I won’t spoil what happens, so go see for yourself.
Note: If you’re having trouble, it may be because you didn’t make at least one save on your fresh install. Save at least once and it should work.