UnknownUnknown
If your monitor is above 1080p you'll need to adjust your desktop resolution in order to play properly.
PROTON_FORCE_LARGE_ADDRESS_AWARE=1 PROTON_USE_WINED3D=1 %command
With resolutions above 1920x1080 (4K for example), the battle screen will be partially offscreen, making them essentially unplayable. You'll need to change your desktop resolution to 1920x1080 BEFORE starting the game. The visual novel sections don't have the same problem though.
I had one random crash in the time I was playing. Beware, this game doesn't have any autosave functions, so if you don't manually save regularly you could lose a lot of progress.
Everything works perfectly after using the flag for wined3d even the in-game videos, opening, etc.
6.18-GE-2 GloriousEggroll
Requires desktop resolution of 1920x1080 or some parts are half off-screen (same on windows), Requires launch options: PROTON_FORCE_LARGE_ADDRESS_AWARE=1 %command% or you will have missing/black graphics at some points. Controller works fine, for keyboard controls see 'view the manual' link from steam store page
