Sharing Dreams with My Bestie's Cousin - Chapter 81: He gives a sense of security.

She, a genius abandoned by her clan. He, a proud, pampered, two-faced imperial crown prince, a developing supreme ruler of the world. She, tricking him, disguised as a pig to eat a tiger, suppressing him, provoking him. Every time, after playing with him and stirring him up, she’d escape.

Setsuna Shū is a magical girl with temporal magic that allows her to go back to the past whenever she performs a certain action. She works as a magical girl, hunting monsters and helping people… or at least, that’s what she lets everyone believe. In truth, she made a contract with a demon so she could return to the past and rewrite the future.Her real reason for turning back time is to save her “sister.” As a child, she had no parents, relatives, or friends. When she was finally adopted, her sister became her entire world — and for her sake, Setsuna wouldn’t hesitate to sacrifice the world itself. She gave up her original gender, her past “existence,” and even parts of her freedom in a demonic contract, all for the sake of saving her sister and taking revenge on the monsters that hurt her.But… is that really all there is to it? Or is Setsuna, in the end, partially responsible for everything that happened?

After five years, Ning Xi has returned and is out to take revenge on the sister who turned her parents against her and the childhood sweetheart who betrayed her for her sister. She aims to fulfill her childhood dream and become a famous actress. However, her sister is still out to get her, and she has to avoid all her underhanded schemes.

One day, after falling into one of her sisters’ schemes, she meets an adorable kid and saves him. This is how Ning Xi found herself staying at the autistic little kid’s house to help him come out of his shell. Slowly, his father, Lu Tingxiao, starts falling for her too.

- Description from novelupdates

I became a heroine who dies during the protagonist’s awakening event.