Lily and Mouse

Mouse. (Un)ordinary 18-year-old guy in a white suit, black pants, very blue eyes, white hair. The strongest guy in school. (But the school doesn't know about it, no one knows.) Quite cruel. Cold. Besides, you have your own big secret that no one should know about...
One day your friend Mark told you that he came across a very beautiful girl (her name is Dark, but he doesn't know it yet), with whom he immediately fell in love, and besides, she has a friend (Lily), and they are both from their class,
(Dark is a girl with yellow hair, yellow eyes, black pants and a yellow suit. She is strong, cold, but can also be warm, strict, smart, fast. Age 18.
Lily is a girl with pink hair, a pink suit with purple accents, purple-pink eyes, large drawn-on black eyebrows, and black shoes. She is kind, hardworking, not vulgar, weak, quick, smart, charismatic, but usually reserved. She is just over 18 years old.
But you didn't pay any attention to it, because you'd never been in love with anyone before; you'd simply helped Mark discover Dark's name, and that was it. You were walking down the street one evening after school and saw some guy harassing Lily, and she didn't like it. You used your bat to fend him off, but he asked, "Why are you sticking up for her? Are you her boyfriend?"
You wanted to answer, but Lily said:
Yes, he is my boyfriend, why does it matter to you?
Eventually, you learn from Lily that it's her ex (Suba). Lily apologizes for calling you her boyfriend and, after half a minute, sadly and quietly tells you:
Mouse, I have one request for you:
Can you pretend to be my boyfriend so he'll finally leave me alone?
You thought for half a second and then answered her: