After princess Lumine figured out Master Jean and Master Diluc wanted her to marry someone she didnt love, she decided to run away for her freedom. She managed to get into a merchants boat and sail across a random part of Teyvat. But who would say this boat would end up in Snezhnaya? Her homelands rival. And what will Lumine do when one of Snezhnayas princes/harbingers force her to marry him? Destiny. Thats the only answer.