Hank Schrader - Breaking Bad. It started out from Ep 1 like “oh, this fucking guy 😒”. By the end of the road I was actually rooting for him. His arc was incredible.

Mr. Peanutbutter from Bojack Horseman. We go from seeing him the way Bojack does, an irritating rival; to seeing him as comic relief; to seeing him as a very relatable, very tragic character who damages all his relationships due to his inability or unwillingness to take responsibility for his own life, someone who has been desperately lonely and depressed but never allowed himself to realize it because he's been masking so hard and so long he believes the mask is all there is.

I've never identified so much with any character on film or television, and it's a fucking cartoon dog.

And then Bandit from Bluey comes along and like the man said, I've only got ten cents but it's weird that it happened twice.

Hunter from The Owl House.
Thought he was going to be the usual overpowered for no reason jerk, but ended up being one of my favorite characters with extremely deep lore and an amazing arc.

Man I love The Owl House so much.

Nynaeve from Wheel of Time. All her quirks become endearing and her growth is so satisfying.

Every single character from Arrested Development.

Renoir from Clair Obscur: Expedition 33. Very misunderstood character at the beginning. And for me, redeemed himself when I started to peice things together. Ended up being one of my favorite characters.

Syril Karn from Andor. From the very first scene he was in, I asked, "oh God, when's this little fucker gonna die?" By the end of the show he was probably my favorite character.

Sally from Barry. I absolutely despise the core of her character but she plays it so well that I absolutely love her too

Jar Jar Binks.

But only after I read this: https://www.reddit.com/r/StarWars/comments/3qvj6w/theory_jar_jar_binks_was_a_trained_force_user/

Dalinar from The Stormlight Archives. At first I just wanted to skip his bits and get back to other characters.

After 5 books, though? One of my favorite characters in the whole Cosmere.

Journey before destination.

Lae'zel from BG3 and Haley from Stardew Valley.

Nathan from Misfits.

I legit hated his character in the first half and ended up loving that rascal in the second half.

The Queen from Once upon a time. She felt more and more human throughout the show.

Scorpius in Farscape.

He was introduced long after the main antagonist, Captain Bilar Crais, was firmly established. Suddenly the Captain was shoved aside for this new monstrous weirdo who's motivation seems a bit contrived.

Scorpius is absolutely fantastic. Wayne Pygram absolutely knocked it out of the park and then some with portraying both Scorpius and Harvey throughout the rest of the series. Probably one of the best written and acted villains in television history.

Well since you named "anything" as an included category, here's a random one: Aila from high rollers: Aerois

For a less obscure one.. Reigen from Mob Psycho 100 ¯⁠\⁠_⁠(⁠ツ⁠)⁠_⁠/⁠¯

Maeve, thought she would be a typical popular girl

Ianthe from The Locked Tomb. She grated on me at first but somewhere into the second book I was just delighted at her terribleness.

Lestat

After finishing Interview With A Vampire and finding out Lestat is the main character of the rest of the series, I was like "well, at least the first book was good, I don't know how I'm supposed to like a book with this douche"

Shortly afterwards: [[Arrested Development meme]] I don't care for Louis

Askeladd/Artorius from Vinland Saga season 1

Highly recommended, by the way

Koutarou Amon from Tokyo Ghoul