As you i have been playing this game for a while and i couldn't find the screen resolution settings because it doesn't exist, so i decided to help you.

There are two ways to change the resolution:

1st Option.
You can change resolution: Go to your library --- > Right click on Ichi --- > Properties --- > Set launch options.

Then in the box add the next command: -screen-width 1366 -screen-height 768
Note: You can change the values at your actual resolution.

2nd Option.
Press alt + Enter twice and the game will auto adjust to your actual resolution.

　
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