Who are Hikaru and Kaoru?
Hikaru's hair is usually parted to the right (from OUR
perspective, but his perspective it's parted to the left) and
Kaoru's is usually parted to the left (again, from our perspective.
From Kaoru's perspective, it's parted to the right). Also, in the
anime, Hikaru's voice is lower, and firmer in the English sub.
Kaoru's voice is higher pitched and softer. Also, according to
Haruhi, when Kaoru isn't with Hikaru, "he is normal and well
behaved, while Hikaru is noisy and has a bad mouth".