I Will Repay My Teacher's Grace with Obsession

*This work is simultaneously serviced with 19+ and 15+ ratings under the same title. Some scenes and story developments may differ depending on the age rating, so please select and use the appropriate age rating. I took in the being who would stain the world with blood as my disciple, and he turned into a madman obsessed with love. I, Gaunsa, possessed the master who taught the protagonist of a tragic Xianxia novel in his youth. What to do with the protagonist, Blood Demon, destined to harbor resentment against the world and eventually destroy it, being so adorable? The disciple I raised with affection and care is terrifyingly obsessed with this master. What should I do with the Blood D...