Blood Sword

Blood Sword is a sword. It grants the wielder a +20% chance of recovering 30 HP per hit they land on a target.

Source
Blood Sword can be purchased from arms vendors in Altissia, Cartanica, Tenebrae, and Gralea for 5,000 gil, or acquired after completion of the Close encounter of the terra kind mission. It can also be found as a collectable in the Crestholm Channels and Pitioss Ruins dungeons. It can be sold back to shops for 2,500 gil.

Trivia

 * There are several weapons that carry some variation of the "Blood" name (and are host to similar abilities) throughout the Final Fantasy series. Fortunately, its FFXV iteration does not reverse its effects upon the user when attacking undead targets (draining the host instead of the enemy), unlike some of its counterparts.
 * The "Dark Knight" is a job class that appears in FFIII and FFXIwho can wield their games' Blood Sword equivalent.