There's many theories questioning what the Darkin is. I propose another that automatically assumes Varus, too, which probably has already been thought of. Like a rework of a champion this suggestion is just the same on lore.
"Only five remain" - Five Darkin or five weapons?
**THE DARKIN BLADE**
_Aatrox - the Darkin Blade_
* The character Aatrox you see could simply be a metaphysical manifestation and personification from the blade itself. _(If you look carefully at Aatrox's features his 'armor' is embedded and ridged like the blade)_
* When there's no wielder of the blade it creates it own wielder as a means to sate itself.
* The living weapon's own Will needs blood to manifest itself its own wielder; itself.
* All that Aatrox is; is the blade.
* The given name 'Aatrox' may actually be the name of the blade.
* This suggests the self-manifested wielder of the Darkin Blade may not have any emotion or whatever; just pure Will.
* _(why would it taunt Tryndamere if this is true?)_
* _(is it preparing Tryndamere to become its wielder?)_
* This suggests the blade may willingly give itself to a wielder whose free will may liberate the blade.
* _(No mind & body is strong enough to wield Darkin Blade?)_
**VARUS AND HIS BOW**
_Many theories already proposed. I'll contribute..._
* Varus is wielding the Darkin Bow.
* the Darkin Bow accepts Varus for his eligibility.
* All that Varus is; is not all of the bow.
* Varus is the wielder. Darkin Bow is Pallas.
* being a wielder stimulates involuntary unnatural psyche as the weapon calls to be sated.
* [important]: Varus' intentions of retribution directly sates his Darkin Bow.
**Eligibility to become a Darkin weapon wielder:**
* sentient mind's free will
* sentient body's durability.
* (Defeat the weapon's own metaphysical manifestation)
* shared purpose consequently sates the weapon
_(like an non-consensual mutual agreement with weapon)_
**Why would a Darkin weapon want specific wielders?**
* wielders grant the weapon the emotions like Love (Varus?) and Rage (Tryndamere?) (and maybe others like Hate) as catalysts to enhance the weapon.
* wielders allow the living weapon to inhibit its endless hunger.
* wielders secure a means for the living weapon to sate itself when it's most needed.
_(kills wielder if its not being sated enough and re-manifests itself its own wielder like Aatrox)_
**Tryndamere to become wielder of the Darkin Blade**
Let's assume you've read all I've written and the Darkin Blade Aatrox is the strongest of the five and no-one is able to wield it .. yet. Tryndamere's rage and hunt for Aatrox could backfire. He'd become an eligible wielder of the Darkin Blade in the end. He may not know this and when a climax between Aatrox and Tryndamere happens he'll be doubly infuriated as it may have been all for nothing. Perfect eligibility.
**Vladimir possibly a wielder of a Darkin weapon, too?**
Possibly not. I considered how his blood-siphoning may work like the Darkin Blade and that there must be a mage-like Darkin weapon (like an orb seems popular on LoL's mages).
The flow of a battlefield could invoke Aatrox to appear. What happens there is something Aatrox understands with clarity: _"I know what lurks in the hearts of men"_. Like a LoL demon looking to sate itself, the Darkin Blade is searching for an eligible wielder or at least set the seed to create one (like Tryndamere). Also to verify the correct wielder may need the candidate to defeat the metaphysical self-manifestation of the weapon itself (in this case the character Aatrox), and this reinforces the idea why Aatrox randomly appeared to find a suitable wielder (in his current background).
**A Demon Analogy (Darkin History)**
Tahm Kench is a demon and he has specific demon-like needs. The Darkin Blade may act similarly but is not identified as demon - more, rather 'demonic'. This similarity between demon and satiation may lead suggest that the Darkin weapons were products of an ancient war and were unrelenting agents among demon army formations (e.g. in Lord of the Rings Helm's Deep battle: Trolls marching with Uruk-Hai). The creators and operators of these Darkin weapons may have been ancient demons. This ancient war is mentioned in Kayle's background. Coincidentally, Kayle's sword is also something special.
**Irelia, Varus and Ionia**
What I've proposed here is the living weapons may have its own Will (if not already) and can decide its own wielder. Coincidentally, Irelia's magic blades seem to withhold that similar idea to this proposed suggestion. Also coincidentally both Irelia and Varus are from Ionia and Varus may be wielding the Darkin Bow.
The similarities here is that Irelia's title 'the Will of the Blades' shares the same idea to this suggestion. The distinction with Irelia's weapon could be as it is stated: "--was the unusual byproduct of foreign intervention" whereas Darkin weapons must be ancient and lacking history. Now, we know-of and acknowledge locations of Valoran have inventors and such... What if Irelia's weapon could ~~be a reverse-engineered Darkin weapon?~~ be the product of a reverse-engineered Darkin weapon?
> **Earlier Things:**
> * a 2013 Thread: [[The Darkin Are Weapons](http://forums.na.leagueoflegends.com/board/showthread.php?t=3567514)]
> * https://www.youtube.com/watch?v=UDrOe4-XdaM
**THANKS FOR READING!** :D