@pizzadude I can reproduce this partially, start button doesn't get the blackscreen go away, but connecting a keyboard and typing z does. Also found that using the volume/steam menu buttons makes the blackscreen go away and also makes it not appear in subsequent launches (seems to require wiping the proton prefix and rebooting for it to come back).
I also haven't gotten the blackscreen issue when using proton 10, have you tried using that version? And if so, have you had the blackscreen issue there?
It might also help to post a proton log too, to help out, i can check and post one later today if needed
@simifor
I can confirm i get the same issue op does when trying it on my oled deck, latest stable steamos, proton Experimental. Loads up perfectly the first time, gets stuck on a black screen all subsequent launches after and the start button does not fix it. Weirdly enough if I swap to desktop mode and then back to game mode, it works again, but only for one launch, going right back to black screen stuck on subsequent launches
This bug is very inconsistent, I can't reproduce it all the time, which is weird, maybe has to do with swapping proton versions.
@pizzadude from what I see, interacting with the steam ui while the game is open seems to make the issue inconsistent to reproduce
@waspennator no matter how many times I try, I haven't been able to get this blackscreen issue with proton 10 or experimental. Wiping the prefix and rebooting haven't helped the issue manifest. For me, when I encountered the issue, the start button wouldn't help, but typing z from an external keyboard made it work for that launch, while volume and steam buttons would also make it work and also seemingly prevent the issue from occurring in subsequent launches
@pizzadude from what I see, interacting with the steam ui while the game is open seems to make the issue inconsistent to reproduce @waspennator no matter how many times I try, I haven't been able to get this blackscreen issue with proton 10 or experimental. Wiping the prefix and rebooting haven't helped the issue manifest. For me, when I encountered the issue, the start button wouldn't help, but typing z from an external keyboard made it work for that launch, while volume and steam buttons would also make it work and also seemingly prevent the issue from occurring in subsequent launches
Still seems to occur for me with latest Experimental after the first boot. I can also confirm that typing z or any key using the virtual keyboard makes it actually work, but it still occurs on subsequent launches.
It also seems like the last good proton version that worked consistently launching for it was 8.0-5, proton 9 introduced the problem somewhere.
Fresh proton Experimental log of my latest attempt where I got past the black screen with the virtual keyboard.
proton experimentalx2 2026-05proton 7.0x1 2025-05proton 9.0x1 2025-05
Compatibility Report
System Information
Steam Deck LCD
SteamOS 3.7.9
I confirm:
Symptoms
On Proton 9.0, after launching the game at least once, subsequent launches of the game on the Steam Deck require pressing a button for the game to actually start (I think it's the start button you have to press) or else it sits at a black screen.
On Proton 7.0 I noticed I didn't have this issue, the game boots up without pressing the start button on the Steam Deck and doesn't hang on a blackscreen until the button is pressed.
Reproduction
Start Mushihimesama with Proton 9.0
Play the game for a bit, then quit (i don't remember if this step is required)
Start the game up again.
Notice black screen.
Press the start button on the Steam Deck.
Notice the game finally boots up.
Play the game in Proton 7.0
Notice you don't have the above issue