This is a cool concept! I don't think I've played a game like this before. The mechanics were interesting, but I think the overall game loop ended up with a bit too much downtime, and the money earned feels pretty slow. I had to play hiroshima quite a few times before getting even one upgrade, which felt like it was too much. Here's a few tweaks I would make:
- Cut back on downtime. maybe you can add the ability to manage at least two "working tiles" at once, just to give the player something to do while they wait up to a minute while the game just counts down. You could toss a slow brushing timer down and then fill your waiting time with faster shovel spots to grind for cash.
- Your first playthrough of hiroshima should give at least enough money to upgrade one tool. Having no level progression and not enough cash to buy upgrades after finishing a level feels like the player wasted their time, or that they did something wrong. Grinding content should pretty much be avoided where possible, and definitely should not be encouraged so early in the game.
- Mention the importance of the brush somewhere in-game. I did not notice that the game was unbeatable without it even after playing for quite a while.
I loved the art and the music, and I loved the concept. I hope you continue with this!