Quick Transmigration: Saving the Tragic Supporting Character

[GB + 1v1] Yun Jin died on the spot in a car accident, then accidentally got bound to something called the System. She was told that if she completed its missions, she could be reborn and her younger brother could recover his health. She agreed at once. Having never dealt with anything like this before, Yun Jin stumbled through her missions. She thought she only had to cherish each target like a younger brother, but the targets developed feelings for her. Her own heart had clearly fallen for them too, yet… She only sees him as her little brother. But... he really is adorable. Why does this person seem so familiar? Never mind, she’s probably imagining things. She’d better focus on her missions.