Fragile Heart

Description
"Increases the health of the bearer, allowing them to take more damage.""This charm is fragile, and will break if its bearer is killed."

How to Acquire
Purchased from Leg Eater in Fungal Wastes for 350. Wearing the Defender's Crest will cause the Leg Eater to lower the cost to 280.

When broken, Leg Eater offers to repair it for  200. Wearing the Defender's Crest will cause the Leg Eater to lower the cost to 160.

Usefulness
This charm is quite potent. It is strictly superior in effect to Lifeblood Heart. For the same charm cost, it provides two regular health points which can be healed by focusing, while Lifeblood Heart adds two lifeblood health that are lost upon taking damage until you rest.

The obvious downside is that you have to return to the Leg Eater and pay Geo to have the charm repaired upon death. Late-game, the Geo may not be much of an issue, but the trip will be.

One way to make use of the charm is to only use it in situations where you are unlikely to die, such as exploration, in tandem with survivability-increasing charms like Hiveblood, while avoiding its use in boss battles. Another is to pause the game when you're about to die and quit to the menu in order to "bench-warp", which makes the charm viable even in boss battles.

In Dream Boss battles, losing the battle will NOT break the charm as technically the player character does not die. This makes Fragile Heart and Fragile Strength incredibly useful for challenging a Dream Boss.

Lastly, it should be noted that in Steel Soul runs, its drawback is completely negated by the fact that when you die, your game is over anyways. Just like Fragile Strength, this makes Fragile Heart significantly more useful during a Steel Soul playthrough.