Nineteen, Twenty-One Series by Yohan, Zhena

Yun-lee is a girl who is carrying a huge emotional scar in her heart. Due to an accident, she lost 2 precious years of her life, the time period between 19 and 21 years old. Her life is empty. She is miserable, but still attending a preparatory school in an attempt to catch up with all the time she has lost. Suddenly, one day on her way to feed some stray cats, she comes across a young man who seems to have what she has lost... the period between 19 and 21 years old.