Byleth gets a tan whenever he/she stays in the sauna for too long. I have a screenshot from my game, but I'm not sure how to hyperlink here.
Edit: Took a look at the screenshot and, yeah, she's red. I misremembered. I know how saunas work and figured the game was using leaps of logic to give the character a tan.
last edited at Sep 9, 2020 3:46PM