Not terribly well optimized, but I suspect that's the game's fault.
Crashed very shortly after first launch, then ran very smoothly after that.
Works flawlessly even at highest settings
Might slow down a little if there are a lot of tiles but that's just a game issue, nothing to do with Proton.
No issues to report
Sometimes gets a little sluggish when there are a lot of tiles, but this is probably a Unity issue. Tested with all settings at high, you might be able to mitigate this by turning the settings down (if it even does anything, which for these hentai games, I'm not sure it does)
Works out of the box
Unlocked all achievements, Steam Controller can be set to use the WASD and Mouse config and it'll work with the game (though you probably won't want to do this). Framedrops when lots of tiles are on screen but that could just be an issue with the game. Doesn't take away from the experience. Perfect compatibility!
Lags a little if there are a lot of tiles and a lot of moving stars. Zooming in usually fixes this. Game can be 100% completed with Proton
Think I got a cramp in my finger playing to write this report from all the clicking. Runs out of the box, no framedrops, everything works, no font glitches or anything. On first boot I got a crash after about 30 seconds of playing, but that hasn't happened again.