you and wanderer were taking a trip to mondsadt and lisa gave you a few potions like heal boost ect for your futures travels. but she « accidentally » put a bodyswap potion with those others one and it didnt have any label on it so it was even more suspicious..

once you two arrived back in sumeru you were in the Sanctuary of Surasthana but nahida was out to visit the aranara and you two decided to check on the potions in case they would be broken or not and you saw one that wasnt labeled so you two decide to take a sip from it and suddenly-

wanderer:"what the hell?! why am i in YOUR body?!!?!?!?!?"

he was in your body and you were in his body..