It's impossible. Quantity of keys is exact the same as the locked doors. You could've missed a key in the bottom left room on the first floor. Also you can buy one if you haven't done it already.
I don't understand how this game is rated so highly. Compared to most other idle games, there's very little player agency or planning involved with anything, and the progression system feels whacky and off.
Player agency:
You don't get to choose skills, you don't (almost) don't get to make any choices in regards to how you get spirits, you don't get to upgrade most of your stats and you don't get to manage almost anything in general. This means there's little to no strategy or thinking involved, which I find extremely dull. I want to feel like my actions matter.
The progression is all over the place. Early game progression easily gets you into the 100's if you spend some of the in-game currency earned via daily quests in an hour or so, which is insane. RPG levelling systems are usually slow or 'deserved', but here, they just count up with little to no effort, which makes it feel less like an RPG levelling system and more like an auto-purchase feature from any other idle game.
Hey there, we're sorry that the game didn't live up to your expectations. This is still an ongoing project and we're still working towards a version of Re:Archer that could provide an engaging and worthwhile experience. You've brought up some good points and we're going to keep that in mind. Thanks for your two cents.
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It's impossible. Quantity of keys is exact the same as the locked doors. You could've missed a key in the bottom left room on the first floor. Also you can buy one if you haven't done it already.