Seduce Me the Otome

Find one of the Incubi. Send the boys away after Malix has gone. When facing Diana, make a deal with her. Choose her, then answer "Yes" to both options at the dining room. When asked about memories, answer that you will stay. When she seduces, say "That's enough!" Take her hand and respond that you should not have to marry someone you do not love. When she take you to the grave, attack her.