Maou-jou no Nisemono Hime - Shujin no Migawari ni Totsuida Kyuuji-gakari ga Shokei Kaihi wo Mezashite Hisshi ni Nattara Maou-sama ni Kanchigaisarete Dekiaisareru Ken

As a substitute for her master, the princess, the maid Elly is married to the demon king. If it is discovered that she is a fake princess, the demon tribe will kill her. She was going to endure only for three years, acting not to be liked and keeping the demon tribe away from her. The more he tries to make them hate him, somehow the more the demon king begins to dote on Ely. Is the love that begins as a substitute real or fake?