
I thought li huan is the only child??

He is. The little girl is most likely the daughter of his cousin. In most Asian countries, cousins are often considered to be siblings and so their children can also be considered nieces and nephews. In the raws, the little girl is just referred to as his niece, there is no mention of sister in there.
ASDFGHJKL AAAAAAAAAA ALL OF THEM ARE GORGEOUS!!! I FEEL SO PROUD READING HAIKYUU AND AAAGAGAHSJSAKAJQOAJSSLAPA I CANT EVEN DESCRIBE MY FEELINGS RN TvT
glad to see that I was not the only one who feel that way