Not a bad premise for a game, but it probable needs some balancing overall. if you are able to bank investment points and armor early you can push through the later fights a bit too easy. I also noticed that even though you can technically place 2 dice in a slot, it only counts the value of the last dice placed.
It would have been good to allow multiple dice in slots so you always have to optimize how many dice you have available for each slot and are forced to make interesting decisions about how many dice you put in each spot. This could create a loop where the player is encouraged to keep buying more dice but you could scale your enemies so that the player could never brute force their way through them.
Good work overall.