If you purchased the game by itself (i.e. not part of a bundle), the Steam key should be available in the download page for the game. If you were logged in when you bought the game, the "Download" button at the top of the page should give you the Steam key below the Itch download links.
Rain Shinotsu
Recent community posts
Hi, sorry for necroposting, but I just tried this on Linux, and I have the same issue. After starting the game, it tries to launch on Steam, but because I got it in a bundle and so didn't get a Steam key, I'm unable to play. In case it helps, I installed and launched the game via the Itch app, and I have yet to try standalone. Still, if you need more info, please feel free to ask.
I'm not daichi, but I can provide a tutorial. Solution below, after the "View rest ↓":
Press the top button -> stop time when the laser is blocked -> jump down -> unfreeze time and press the lower button to create a heart block -> move the heart block to the left trampoline and get it to bounce -> jump on the right trampoline, timing the jump so you pass by the laser as the heart block is blocking it.