After Rebirth, My Junior Sister Snatched My Position as the Devil's Concubine

In order to be selected as the Demon Concubine, my junior sister and I entered the secret realm. In my last life, I accidentally found the secret medicine and became a witch who could give birth to a demon fetus; but my junior sister failed to harm me and was backlashed by the secret realm, turning me into a furnace for the demons to nourish themselves. I was chosen by the Demon Lord and became the most noble woman in the Demon Clan, while my junior sister could only be locked in a dark dungeon and used for training. Later, when the demon king unified the six realms, my junior sister used the excuse of congratulations to approach me and ended my life with a glass of poisonous wine. After rebirth, we once again returned to the day when we entered the secret realm. At this time, junior sister found the secret medicine first. "Sister, this time it's your turn to be harvested day and night!" I happily jumped into the trap she had set for me. The Demon Lord is cruel and cold-blooded, and being his woman is not an easy job.