The Japanese version mentions Haku as Chihiro's boyfriend
The scene where Chihiro visits Zeniba and asks the witch for help. Zeniba says that she can't and that Chihiro has to save her parents and her boyfriend on her own.
In the English dubbed version, there was no mention of the word 'boyfriend' and Zeniba said Haku's name.
Either Zeniba was just being playful calling Haku as Chihiro's boyfriend or the Japanese writers originally planned a romantic link between the characters.
I'm just glad that at the end their relationship was cemented to just being friends and there was no goodbye kiss cause that would just be too Hollywood.