He doesn't mean what he says (he is a coquettish person in the later stage)
Xu Daoxia never felt that she had any feelings for Xu Zhiqiu other than brotherly love.
But Xu Zhiqiu always made his heart beat. It was true ten years ago and it will be true ten years from now.
So after careful consideration (bingmeiyou) decided to chase people.
Xu Zhiqiu admitted that even ten years could not make him forget Xu Daoxia.
Really. He also said that he would chase himself.
Chase, chase. If I can't catch you, I lose.
Purpose: Brothers and sisters respect each other and live happily together as a family