The user can manipulate aversions, thus controlling/changing what a person or thing's power or attributes are weak to. For example, this can change one's aversion to fire to one of water, or change how much weaker they may get when they are exposed to something.
In most cases, this power manifests in the form of power sets that directly relate to or manipulate others' aversions.
Himegami Aisa's (A Certain Magical Index) power, Deep Blood, attracts vampires to her blood...
...and kills them.
As bearer of the Nemetrix, Zed (Ben 10: Omniverse) can turn into the natural predators of the Omnitrix aliens, making her a perfect counter to Ben Tennyson.
Duke Nukem's (Captain Planet) power over radiation makes him a deadly opponent to the pollution-averting Captain Planet.
Captain Planet and Captain Pollution's (Captain Planet) powers directly counteract each others, as Captain Planet is weak to pollution and Captain Pollution is weak to pure elements.
Created from pure Innocence, Apocryphos (D.Gray-man) is specifically designed to kill Akuma and Noahs.
As a repatriate, Sam Porter Bridges' (Death Stranding) bodily fluids can counter BTs and send them back to the other side.
Conduit (DC Comics) hitting Superman with Kryptonite radiation.
By actively capitalizing on his Reactive Adaptation, the Devastator (DC Comics) has tailored his powers to Superman's weaknesses.
Enzyme (Guyver) produces corrosive enzymes that specifically counter and dissolve the Guyver's armor.
Angra Mainyu (High School DxD) wields Dragon Slaying Magic, a form of magic specifically created to slay dragons.
Firestorm (Injustice) generating Kryptonite radiation to weaken Supergirl.
The Ripple (JoJo's Bizarre Adventure) channels energy identical to that of the sun, making it the perfect way to combat creatures like vampires, zombies, and the Pillar Men.
X-Ray (Marvel Comics) can generate "anti-gamma radiation" that can depower the Hulk and revert him to Bruce Banner.
As a master of magnetism, Magneto (Marvel Comics) is a particularly dangerous opponent to those with metal in their bodies, such as Wolverine...
...and the Predator X's.
Kaine Parker's (Marvel Comics) Mark of Kaine makes him a fearsome opponent for heat-averting symbiotes like Carnage.
Spider-Man's (Marvel Cinematic Universe) spider-sense makes him the perfect counter to Mysterio's illusions, as they only affect normal senses.
Samus Aran (Metroid) regularly makes use of her Ice Beam to combat the cold-averting Metroids...
...and after being transfused with Metroid DNA, she gained the power to assimilate and kill X Parasites by physical contact, as the Metroids were the X's natural predators.
Monkey D. Luffy's (One Piece) rubbery body makes him the perfect counter to the electrical Enel.
Scissors' (Paper Mario: The Origami King) very nature makes him a deadly opponent to the residents of the Paper Mario world.
After undergoing LuthorCorp's Project Prometheus, Lana Lang (Smallville) gained the power to absorb and emit Kryptonite radiation...
...sadly making her unable to continue being around Clark.
Kuyo's (Rosario + Vampire) fox-fire makes him an especially deadly opponent to the heat-averting yuki-onna Mizore.
Ruby Rose and Maria Calavera (RWBY) are Silver-Eyed Warriors, wielding a great power...
...that makes them the bane of the Creatures of Grimm.
Megatox (Sonic the Comic) is composed of and manipulates Mega Mack, a toxic chemical specifically designed as a weapon against Sonic.
Red X's (Teen Titans) suit and main weapon systems are specifically designed to combat all of the Teen Titans barring Robin.