Nice game and really cool idea with the platforms which exist only on one side. I also liked the shop with the upgrades very much. I think it would be more intuitive if the controls in the shop were also using the movement keys (a /d and maybe enter to buy). Fighting with the arrow keys is new to me and a nice idea, but I think it would feel better if the spirit has a moving direction and you have only one key to attack. The spirit would then always attack in the direction which it is currently looking. This would add an additional challenge. By the way, the attacking is not mirrored. I think it would have made more sense to also mirror that.
Congrats to a cool game!