I was looking at the Guardian fighting style, and it's a really cool idea, but also really broken.
My issue is that at 20th level, you could take 45 points of damage every round for free, and you can do it on someone else's behalf. You can move around the battle really quickly to intercept attacks, and you can do it without losing your movement at level 7.

It's a good idea, but I think that the Charge feature should only be available for use if you didn't use the Lunge feature that round, and I think that the Ward should take 10 minutes of concentration to regenerate. This way, it can't be abused in battle, but is really good for defending your allies outside of combat.

In my personal opinion, I think the Ward should be more similar to the Monks Deflect Missile, in that you make some sort of roll to reduce damage, rather than absorbing it with a pool of hit points, but I understand where you were going with this.