The Guardian excelles at offering protection and defense to weaker allies on the battlefield.

Intercepting Shield

Allies with maximum hit points lower than your maximum gain advantage on saving throws as long as they are within 10 feet of you.

Whenever an ally with fewer maximum hit points than you are that target of an attack, if you are wielding a shield then you may use your reaction to reduce that damage give that ally +2 to their AC until your next turn. They lose this bonus if they move more than 10 feet away from you. If the attack still hits then you may reduce the damage by 1d10 plus your proficiency modifier.

Bonus Profeciency

When you take this subclass choose two from among the following list: Insight, Investigation, Medicine or Perception. You gain proficiency in those skills.

You automatically learn the Protection Fighting Style 

Bolstering aid

If an ally with fewer maximum hit points is within 10 feet of you when you use Second Wind, their maximum and current hit points increase by 1/2 your roll for 10 minutes.

Take the Hit

If an ally with fewer maximum hit points than you would be caught in a Line or Cone effect, you may use your reaction to place yourself between them and the effect's point of origin if you have the movement speed to do so. If so that ally gains a bonus equal to your proficiency modifier on any saving throws. When they would make a saving throw to take only half damage, they instead take no damage if they succeed on the saving throw, and only half damage if they fail. You have disadvantage on your Saving throw against the effect.

If an ally with fewer maximum hit points would be caught in a Circle effect, you may use your reaction to travel to them and pull them towards the outer edge of the effect. You do not suffer a movement penalty when carrying them this way. Even if you were outside of the circle when it was cast, you take any damage and are subject to any saving throws or conditions inside of it.

Intimidting Distraction

Whenever an enemy makes a successful attack against an ally with fewer maximum hit points than you within your sight, you gain advantage on attacks against that enemy on your next turn.

Whenever you score a critical hit on an attack against an opponent, they have disadvantage on any attack made against your allies until your next turn.

Lightning Reflexes

You may use 2 reactions per round instead of 1. When you roll Initiative, you can add your Proficiency Bonus to the roll. Immediately after you roll Initiative, you can swap your Initiative with the Initiative of one willing ally with fewer maximum hit points in the same combat. You can't be surprised while you are conscious.