Hoshikusu to Hanayome

Loletta is a bride-to-be from a tiny island nation. In order to ensure the welfare of her adopted family, she decides to marry a rich man she doesn’t love. In preparation for the marriage, a mysterious man who calls himself Kuzu shows up, claiming that her dead brother gave him his heart on the condition that he fulfills a promise made to his beloved little sister. Upon hearing this, what is Loletta supposed to do?