After trying to draw the attention of the oblivious emperor for a year, Nuriko fumed as he saw it devoured by the new miko. In a jealous rage, Nuriko persued Tamahome instead to get back at her and spurned Miaka's attempts at friendship.
Although the teasing never really stopped, Nuriko's feelings definitely took a more benevolent turn. While Nuriko was insanely jealous, he still had a conscience. After all, if he had really wanted to get rid of her that badly, he could have simply allowed her to be crushed by the building. But Miaka's continued efforts to befriend him eventually took their toll. Nuriko grew fond of her, and grew comfortable with his duty as a seishi.
They eventually developed something of a sisterly relationship. Miaka's relationship with Nuriko reveals wonderful facets of his nature (such as his protective and playful qualities) despite the bad beginning and eventually leads him to discover his true self (more about this on this page).
[SPOILERS, 30-something +...]
As for Nuriko's falling in love...
Well, it reveals what a sweet person he is to simply want Miaka and Tamahome to be happy despite his feelings (oh, what a gracious person!-p). At the same time, it's so contrived that seishi after seishi winds up falling for Miaka! And how many unrequited loves does Nuriko need, anyway?
Priya thinks that Nuriko wasn't really in love with Miaka--that it was a more platonic relationship. The evidence supporting this would be the fact that Nuriko didn't grow all that jealous over Miaka. Nuriko seems to have more of an older sibling relationship with Miaka, and that doesn't really change after he announces that he's in love with her. Perhaps Nuriko was attracted to the qualities in her that he missed in his sister.
I personally don't care whether people believe that Nuriko was truly in love with Miaka or not (although I lean toward the more platonic love idea just because I dislike the Tenchi syndrome [see the rather overrated series if you don't know what I'm talking about]); their relationship's still fun, and the sentiments behind it are similar whether Nuriko loved Miaka in a romantic way or not.
so that's that...
At first, he hated her.
©1999shilpa & priya