First off, this game has some visual flare! I do see the connection with Undertale but I think you definitely add in your own touch too. To me the connection to "less is more" here feels a bit tacked on and farfetched, feels like you came in with an idea in mind that you wanted to follow instead of finding something that works with the theme. Not necessarily a bad thing though!
The text speed felt too slow for me unfortunately, I would've played the game a few more times if there was an option to make the dialogue appear entirely by pressing space again :(
The variety in attacks and themes is pretty welcomed. Some attacks feel a bit unfair and hard to telegraph though, either having more warnings or seeing them outside of the box before they come in could go a long way in achieving a better game feel.
All in all, there is a lot of potential and charm in this game, although it could really use some small tweaks here and there to make the experience really flow. Well done!