Recently Brokenpeanut67 (httpss://www.twitch.tv/brokenpeanut67) found a fix for certain fangames not working on Windows 10.
EDIT: On 9/5/16 I made a simple program to apply this fix to all exes in a folder. Scroll down to that post for more info.
Here's downloads of fixed exes for Cultured (httpss://www.mediafire.com/?blke472dd88z64c) and Genki (https://www.mediafire.com/download/4qhpgeb96m4xr80/I_wanna_be_GENKI_with_you_%5Bfix1%5D.exe) so you don't have to do it yourself (put the exe in the game folder next to the old exe). The steps are listed below for the sake of documentation. Please post if the fix works for any other fangames.
1. Download and install CFF Explorer https://www.softpedia.com/get/Programming/SDK-DDK/CFF-Explorer.shtml#download
2. Right-click on the game exe and open with CFF explorer. Click "no" to dialog.
3. (https://i.imgur.com/lySvezH.png)
Click "File Header" on the left, "Click here" on the right, check "App can handle 2gb address space", click ok. See the screenshot.
4. Save the exe, and try running it.