One can voluntarily pay for the game when you click download to support them. I did it, and I gave them a Haiku which they added to the bathtub scene in the game (shows up randomly).
Thank for reply. Given that the song is not my original composition and possesses a distinctive style—which I greatly admire and believe to be well-suited for this game—I feel it would be more appropriate to ask for dev's opinion first.
Additionally, I am certainly willing to make a donation, but I am uncertain about the appropriate amount for this situation😄️. Btw, here is the video link for reference. If you can't open it, there is also an MP4 version available.