Koujaku has changed, and he hasn't.
He has changed in obvious ways - the length of his hair, the sword, his way with women - and in not so obvious ways - the way he clutches secrets, how tension seems to rise when he's in close quarters with the posse Aoba has acquired somehow, how quickly his anger rises - these traits are all at once Koujaku, but also not. Aoba can't fathom how like Koujaku he is and isn't, but somehow the conflicts cancel each other out and create the hairdresser in front of him, the same child he knew that comforted him so many years ago when Tae had left him alone in that park for so many hours.
Aoba thinks that Koujaku is like the edge of his sword, in some ways. One side is smooth, pleasant, welcoming - this side is reflective to show the whiteness of his grin, the purity of his mirth. The other side is the edge, sharp, made to create clean cuts that will sever everything, even the deeper bonds. Some days Aoba can't help but wonder - why? Why is Koujaku his sword? Why is that the closest thing he can compare the man to? He has never been on the wrong end of it before, yet he wonders if it is too soon to decide that.
However, it is the way that Koujaku teases him and reassures him with such jokes that lets Aoba know he is not quite a sword. Perhaps he is a swiss army knife, with many tools and talents... but there is always that one knife, the one weapon that cuts unexpectedly hidden in the folds of the other tools. Koujaku is a man of many talents, of many faces, and Aoba isn't very sure he has seen all of them, nor that he wants to.
But he enjoys this Koujaku, the one who calls him names just like they are children. This Koujaku supports him no matter what, the first to place his trust in Aoba no matter the situation because he already has it. Change or not, the man in the red kimono has always been his ally, his closest friend despite secret doubts. This Koujaku is the constant in his life, and he would do anything to keep him safely close to him, within arm's reach. This Koujaku reaches for his hair and grins when Aoba shivers at the bolt of sensitivity that races through him.
This Koujaku is his best friend, Allmate aside, and Aoba finds himself at peace with this. He loves Koujaku, confusion and all, his many faces, sharp edges and unpolished facets. He loves even the parts that flirt with women, that leap at the chance for a fight, and Aoba wouldn't trade any of it for something better - because then it wouldn't be Koujaku.
And he needs Koujaku.