The Cannon Fodder Side Character Just Wants to Quietly Follow the Plot

Han Li transmigrates into a book. Because she accidentally touched a strange man's butt, she gets thrown into an erotic novel as a cannon-fodder female character... The man tells her she has to wait until the male and female leads get married successfully before he can send her back. If she dies before then, she'll die. If the leads don't get married, she'll die. If either lead dies, she'll die too! In short, her life is tightly bound to the main cast. Even a grain of sand on one of the leads could become the mountain that crushes her fate. But in theory, this is just an ordinary Mary Sue story. The leads may face a rough path, but unless something goes wrong, they'll have a happy ending. And Han Li's new identity after transmigrating into a book is pretty good. She can lie flat and still live well. After enjoying herself for a while, her parents bring home a child from outside. They say the child is pitiful and all alone, so she'll be staying with their family from now on. When Han Li learns the child's name is Tan Luofei, she realizes she's met the one and only love of her life, the heroine of the book, the woman she's meant to serve for the rest of her cannon-fodder life. "Leave it to me!" Han Li immediately takes the heroine's hand, drops to one knee, and kisses the back of it. "Oh, beautiful Fei, from this moment on, you are the faith of my life and the soulmate of my spirit. I will protect you as I would the moon. I will love you until the end of my life..." For some reason, the heroine's face turns red, then dark, as Han Li makes her vow. Meanwhile, Han Li gets dragged away by her parents, who twist her ear. But that little lesson does no good. For the next three years, Han Li is always by the heroine's side, kissing and hugging her, building affection and making sure she's noticed, while helping her deal with a few villains who don't know their place. Until one day, her parents bring home another boy. He's the only son of a domineering, obsessive CEO. He's handsome and ruthless, cold and heartless, and according to the story, he'll one day become her boss, the kind of man who has the final say. Han Li gets the message and immediately takes the male lead's elegant hand, drops to one knee, and kisses the back of it. "Oh, esteemed Chun, you are my life's guiding star and my lifelong idol. I will serve you and remain by your side for all my days, until the end of my life..." This time, the heroine, her expression twisted, grabs Han Li by the ear. Hah, she's jealous. Han Li shakes her head in dismay and gives a helpless smile. This is supposed to be the first meeting between the cannon-fodder character and the male and female leads, but the leads nearly come to blows. Han Li remembers that it was raining hard that day. The future leads, whose story will drag on for eight hundred chapters, glare at each other, evenly matched in presence. Han Li vaguely sensed something was off at the time, but she didn't think much of it. Until one day, the heroine cuts off her long hair and reclaims her identity as the eldest son of an aristocratic family. Han Li breaks down. Wait, what? Where's her heroine? Where's that gorgeous, fair-skinned heroine with long legs and a tiny waist??? Note: One-sided feelings, love triangle drama, Mary Sue Theme: Be brave