an interesting topic
the most recent character off the top of my head would have to be Ray Lundgren from gun x sword. initially portreyed as cold, and heartless (though not without reason) he even shuns his own brother in order to carry out his revenge. as annoying as his brother was, it was one of the main reasons why i detested his personallity.
as the anime wore on, especially towards the end, he really showed that he had matured, and without getting too spoily, his departure from the anime was one of the sadder moments.
its surprisingly hard to think of anime with "authentic" character growth... but maybe "initial reaction" could be changed by factors other than development of character, such as revealing of background story?
i'll be sure to post if i think of some more ^^