I was Told to Relinquish My Fiance to My Little Sister, and the Greatest Dragon Took a Liking to Me and Unbelievably Took Over the Kingdom
Even though she has been training to become the crown princess her entire life, her spoilt, less capable (useless), younger sister takes her fiance in a tantrum of "love at first sight". Losing her sense of self-purpose/care, she offers to be the dragon's bride, and throws herself in the volcano in which he resides, surrendering herself to her demise. In actuality, the dragon is real, accepts her proposal, which somehow leads to him conquering a neighbouring kingdom. Her dragon fiance gives her full reigns to rebuild and rule the nation's affairs.
The Pet of the Villainess Webtoon
Sasha resigns herself to be the pet of the nobles in order to live in her reincarnated life. Since she has already known the timeline of events, she plans to be friends with the heroine and avoid the villainess. However, after meeting the villainess, Sasha decided that she'll devote herself to making the villainess happy, even if she has a bad ending.
Death Is The Only Ending For The Villainess
The angst (♡~♡) yes plsss~
Koushaku Reijou no Tashinami