I'm looking for (preferably) Main Characters that are specialized in defending and countering, instead of attacking. Those that await the attack of the enemy, only to dodge/block and counter. Thanks in advance.

The only one I can think of atm is Shura no Toki. They dodge the first sword before attacking generally.

If it's not limited to fighting, I suppose ones like Kurosagi?

________________

The first that comes to mind is Miyata from Hajime No Ippo. Not the protagonist, but the main rival who's specialized in counter punching.

Other than that you could also check mangas about aikido, which is mainly about redirecting attacks, and momentum :
Aiki (not very realistic and it doesn't really focus on aikido)
Evil Heart
Hana no Miyako!

Kurogane (IKEZAWA Haruto)

all I can think of right now, sorry

I might remember wrong but there's no martial arts as the OP wants in this, it's mostly armed combat in a siege, and focuses on strategy/tactics in antique asia. I get the defensive style (the MCs do defend a fortress after all), but as I understand it the OP wants something more individual...

Right, didnt pay attention, start off as pure-stategy, then gets a bit more into characters, but martial arts is barly themed, great manga though

Go to youtube and start watching Juan manuel marquez or Floyd mayweather jr fights.

________________

Not a manga but a OEL webcomic Flipside, the mc does absolutely no offensive tactics, she only counters.

ABSOLUTE DUO mc weapon is a shield