5 years late, but you don't even need a plugin! Just upscale the assets to 48x48 (x3 scale), it can be done easily in any software like Aseprite or Krita. I used the assets for a RPG Maker MV game (https://juan-muela.itch.io/the-brief-and-cruel-life-of-a-recently-spawned-slime) and it all works perfectly! So I fully recommend buying the assets if you are using RPG Maker!