A/N: Watching Ouran videos apparently does this to you.
It broke his heart when Hikaru dyed his hair black. He was glad that Hikaru had found his own identity, but he thought they were just fine before.
When it had only been the two of them (and a girl Kaoru liked to forget) who had been able to tell them apart. When it had only been the two of them (and her), who had known that they were different, and not similar on the inside, too.
When Hikaru didn't need anyone else (her) to tell them apart. Kaoru knew that he had done it for her, because he hadn't done such a thing before she came into their lives.
Before her, it hadn't mattered that no one could tell them apart. Before her, no one else had mattered.
It had only been the two of them, and they had laughed about how no one was able to tell them apart. But now Hikaru needed her to know that he was different, to know who of the two he was.
And Kaoru hated her for it, for his black dyed hair.