Master, Let Go of Your Tail

【Transmigrate into a book + matriarchal world + devoted couple + parallel world + a husband who keeps his wife on a tight leash】 【Yandere master wife × a husband who says one thing but means another】 The last wish Gu Chi made on his birthday was to have a yandere fall in love with him. But is it really a good thing for a yandere to fall in love with him? Gu Chi transmigrated into a book and became a cannon-fodder character. His master, the Demon Lord who ruled the demon world, was a bloodthirsty fiend. As her disciple, how could he possibly be killed by someone else? It was because he disobeyed his master that he ended up dead. As for why, the author never explained, only writing that he was killed for being disobedient. When Gu Chi learned that he had become the Demon Lord's disciple in the book, he immediately wanted to find his mother. After leaving, he suddenly realized how pitiful his master was. No one had cared for or loved her as a child, and her parents had even sold her to a brothel. The original character, whom she had once saved, was taken in as her disciple. If he left in the original character's place, how would his master go on living? So he returned to the demon world. His master locked him in a dark room day and night. In the days that followed, his master didn't mistreat him, and he was quite satisfied, so he married her! But after they got married, his master seemed to grow more and more deranged! …