Slime Taikou to Botsuraku Reijou no Angai Shiawase na Konyaku

When her sister's engagement to the Crown Prince is broken off, ducal daughter Francesette is left with no family to look after. Despite her poverty, the ever-positive Francesette makes the most of her baking skills and begins to live at her own pace in the downtown area. One day, she picks up a weak slime on the street. This leads to a proposal of marriage from Gabriel, the Grand Duke of Slime, one of the "Demon Lords"...?