This is amazing, the art style, the game mechanics, the aesthetic, it all gels really well together to make a very relaxing game! I would suggest totally continuing to develop this idea further and you'd have a marketable game. Some things I'd do to improve the game would be allowing the player to sell cards from their inventory (since it's a bit rough when I want to sell my inventory cards to buy a new shop item but I can't select cards from my inventory to sell) and maybe allow the player to keep mana between turns instead of resetting it. I really enjoyed this and I think you did an amazing job on it! I look forward to your future projects and games.