So here's what I THINK
you play as YOU
you enter an abandoned Monogon simulation (idk why), that being FantasyLand
You enter, and a villager (determined by your dice roll) is chosen as your vessel
but in FantasyLand, since abandonment, they have developed "commandments" of sorts
one of them is rejection of modification to mind, body, and spirit. When you enter a village, you are modifying them, so you're instantly excommunicated
basically long story short, you're YOU, and you can canonically change your body