Mutual devotion, an older woman and younger man, a sweet little romance.
Wu Xun, 18 years old and 184 centimeters tall, was a high school senior before the apocalypse. He'll grow a little taller later.
Chang Xing, 21 years old and 176 centimeters tall, is a perfect experimental subject who has undergone genetic modification since childhood. He escapes the lab when a virus leak allows the infected to break in.
On the day the apocalypse begins, high school student Wu Xun saves a child. While carrying the child, who has turned into a cat, and fleeing the infected, he is bitten.
Before Wu Xun can mutate, the little cat saves him. This strange child can actually cure the virus, and has also bound Wu Xun to a bizarre symbiotic contract.
The child isn't a child, and isn't a little cat either. His true form is a young man three years older than Wu Xun.
I can't think of what else to write. Anyway, this is a brainless, sweet little story I'm writing to feed myself.