Killer's Blade is a skill located in the Assassination (which can be found in the Nightblade skill tree). Killer's Blade is a morph of Assassin's Blade.
Killer's Blade deals the following types of damage: Disease Damage. Which means that it gets buffed by the following blue champion point trees: Blessed, Master at Arms, Mighty, Piercing, Precise Strikes, Quick Recovery. Also the following red champion point trees protect against this skill: Hardy, Iron Clad.
ESO Skillbook