How fitting

[Shurrikhan]

WAR wasn't capable to siphon life energy from anything. That art belong to DRK.

DRK in...

• FF2: Starts with a broadsword and buckler. Top proficiencies are with (one-handed) swords and axes. Some lore implications of mind-influencing capabilities. No lifesteal capabilities.
• FF3: Can sacrifice HP to deal AoE damage. Can use White Magic. No lifesteal capabilities.
• FF4: Can sacrifice HP to AoE or, in later versions, to double its attack (at HP cost per attack). No lifesteal capabilities.
• FF10-2: Excels in raw physical damage (albeit at low speed) and applies status effects such as Bio, Doom, and Blind. Immune to Poison, Petrification, Confusion, Curse, and Doom/Death. Can sacrifice health for a ST nuke or to AoE. Can cast Arcana spells. No lifesteal capabilities.
• FF The Four Heroes of Light: Sacrifices HP to deal additional damage. Deal increased damage as %HP decreases. No lifesteal capabilities.
• FF13 Lightning Returns: Can sacrifice HP for additional damaging effects. No lifesteal capabilities.
• Dissidia 2008: Just a slower, hard-hitting attack mode for Cecil. As an AI job, it is a stepping stone leading to Mystic Knight and Berserker. No lifesteal capabilities.
• Dissidia 2012: Simply adds an HP-sacrificing Attack, Shadow Bringer. No lifesteal capabilities.
• FF Airborne Brigade: Requires BLM and WAR. Sacrifices HP to deal additional damage. No lifesteal capabilities.
• FF Tactics (WotL): Drains HP or MP to maintain a throughput-increasing buff and can sacrifice HP to deal additional damage. Can absorb both MP and HP.
• FF Dimensions: Sacrifices HP (Darkness or Onyx Wave) or MP (Ebony Slash) to deal additional damage. Lifesteal effect only affects auto-attacks, at a mere 10% of damage dealt. Increased relative range via the Backliner trait.
• FF XI: Has access to Black Magic, though less than as available to BLM or even RDM. Can sacrifice HP to deal additional damage. Can mimic the effect of wielding a Blood Sword via the Blood Weapon skill once per hour, gaining health equal to damage dealt with basic attacks.

That's 3... out of 12 games with a playable "Dark Knight". But, sure, let's pretend lifesteal is somehow long-historied and exclusive attachment to DRK, let alone more integral or prevalent than HP-sacrificing skills such that XIV's lifesteal capacities ought be exclusive to DRK (even though Warrior, historically, sees as much use of lifesteal and they're both outdone by any Black Magic casters in games where Drain is a player-accessible spell), while lifesteal itself has been given to many a character that has nothing in common with DRK...

:: Side-note: the most repeated user of a "Blood Weapon" skill (even when limiting such to its HP-absorbing functionality) is... Firion, who is typically presented as an agile bow-, sword-, and spear-user in light armor.