It's canon to the Ultimate Note series.Xiazi shows his eyes behind his black glasses only in very serious situations.Also,Xiazi has some kind of suicide mode on sometimes.That is why Xiazi stays with Xiao Hua the most,to have someone who can call him down.

Xiao Hua is respectful and serious while Hei Xiazi is the opposite.

Xiazi always follows him around,even when Xiao Hua isn't in danger zone.They have short arguments sometimes, not bad.

One day,while Xiao Hua was having dinner with Xiazi,he noticed something rather odd.Xiazi was quietly eating,.. quietly..which was uncharacteristic of him.He would take every chance to tease or just simply talk nonsense with Xiao Hua.Xiao Hua glanced at Xiazi and suddenly his eyes widened.Xiazi lifted his hand and began taking his black glasses off.

(You're Hei Xiazi and male.)