You're right, I think it was the death/fail screen that confused me a bit on the story; "succumbed to the demon's mockery".
Using "motivation" as health is a good choice, it makes total sense, and that was the only reason I reacted to the "koin" part as that works as the players motivation and in dissonance with the rest of the game. Not so much criticism as an observation.
I like the idea of like Sisyphus rolling the rock up the hill, maintaining your motivation despite constant pushbacks and regressions, and doing so by improving your perception of yourself (adjectives or properties like "self-worth", "pride", "humility", "introspection", "empathy" etc.)