Tis true! If you think about it, Fai really is the seme in the KuroFai couple! Which technically means it should be FaiKuro... But KuroFai sounds better. For you peeps that have no clue what seme is:
Seme: Japanese for the dominant in a relationship
Uke: Japanese for the recessive one in a relationship
Also, if you've know anything about Tsubasa, most people know that Kurogane hates cute nicknames. But if you notice, I don't think he's ever used anyone's real names!
Just another reason why KuroFai is TOTALLY cannon!
P.S. Dedicated to my friend superyaoidobe. She just started reading Tsubasa and she already agrees its totally cannon!