
Wait...does that mean He Tian also the uke??

You forgot the setting is in China. And the manga is chinese.

This is only in Japan, but I do want He Tian to be uke (=・ω・=)

No the op's right, white day exists in china too. The tradition's origin may be from japan but it eventually spread to china etc. Source: i lived in hangzhou for almost three years :-)
And topic related: whaaat? I can't even imagine them as a reversible couple :-D

actually boys and girls can give choco on valentines day. the return day white day is the same. its just more common for girls to do the first choco gift.
In Japan/ China, girls give their love interest some chocolate on Valentine's Day, and boys will return the favour on White Day... which makes Zhan Xixi the uke... Sensei, is this a hint? Ho ho :3