Barbarians who have mastered their own vitality and the vitality of others can utilize this power in battle, as a Hemo-Fury barbarian.

Crimson Rage

While you are raging, the first time you hit on each of your turns takes an additional 1d4 necrotic damage and you gain temporary hit points equal to half the necrotic damage dealt. Temporary hit points gained with this, or any other feature of this subclass count as coming from one source, and are all lost when your rage ends. This necrotic damage increases at certain levels: to 1d6 at 5th level, 1d8 at 9th level, 1d10 at 13th level, and 1d12 at 17th level.

Additionally, on any attack you make while you are raging you may deal an additional die of necrotic damage (of a die size as determined above) and gain temporary hit points based on that damage (as ruled above), but to do so you must take that same die worth of damage (which takes directly from your hit points, regardless of whether or not you have temporary hit points), which can not be reduced in any way.

Bolstered by Blood

When you rage, you may expend any number of hit dice to gain temporary hit points equal to the total roll on those dice.

Additionally, before you attack while raging you may increase your attack bonus for that attack by 1 or the damage for that attack by 1d4 of the weapons damage type, but to do so you must sacrifice 5 temporary hit points. You can do a maximum number of times equal to your proficiency bonus per attack.

Vitality Cycle

You have resistance to necrotic damage. At the start of you turn while you are raging, if you are below half your maximum hit points, you may regain a number of hit points equal to your proficiency bonus.

Additionally, while you are raging you may spend a bonus action on your turn to lose all your temporary hit points and regain a number of hit points equal to half the temporary hit points you just lost.

Hemomantic Avatar

When you enter a rage you may expend 5 hit dice to become a enhance that rage. While you are raging in this way, each attack you hit deals one additional die (of a size determined in "Crimson Rage") plus your proficiency bonus of necrotic damage, and you gain half of that necrotic damage worth of temporary hit points. Additionally, if you are below three-quarters of your maximum hit points then you regain hit points as per the "Vitality Shift" feature. If you are at maximum hit points at the start of each turn then you gain a number of temporary hit points equal to your proficiency bonus.