Minato Gensou ~Venice Fantastica~

The protagonist is the son of a noble family, who, unable to agree to be part of a political arranged marriage, runs away. Without a place to go, he eventually arrives at a place of a baroness who is a long associate of his father. Hearing his story, the baroness offers him room and board. In return, she requests that he take over the worldly education of three girls under her care. Two are merchant and noble daughters preparing for marriage; the third is a prostitute from a foreign country.