Two spirits/creatures who are or at least think they are the essence of death, granting "fate" to poor random bastards who get their "mark", who also enjoy watching things die.
This champion is a Serial Killer is basically what I'm trying to say. 
2.0
Death is not evil.
So what about 
the guy who kills people and tortures their souls for FUN
Or 
who tricks people into making a deal with him only to make them suffer,by taking away all thats dear to his "partner",because he enjoys their despair.
Meanwhile kindred seems to be more a force of nature than a person.
I mean you're not wrong, though. Death is technically the most prolific serial killer in history with almost a 100% success rate (with a few outliers depending on your particular faith system).
There is nothing inherently good or bad about death, its just there as a natural force in the world, which is represented in the appearance of Kindred.
Tahm Kench is a demon, he is evil.
Death is something natural that must happen to all the living creatures, its not evil.
is the most evil champion.
uuh what about elise who yearly lures people to get ate by a giant spider so she remains immortal, or how about shaco who is almost a serial killer. then their is fiddlestix who was summoned by an insane summoner who whenever someone tried entering the room where he was someone either was killed or chased out by crows having months of fearful visions of crows for months. then their is mordekaiser who to lure is on a never ending quest to go and kill everyone for information to find out in horrific ways. then their is draven who is an executioner for noxus that his idea for a good execution is letting people attempt to run to freedom just right when it is a few feet away he spins both his axes forwards murdering them.
In game for clarity we're marking enemy and it causes to look an asssasin killing for fun, but as we know lore and game is so different. What if Kindred is hunting the enemy who they time came? Like real Grim Reaper, don't kill anyone without their time has come.
