The user can inflict an enormous level of agonizing damage to the soul of an opponent which not only damages the spiritual being of an opponent but their physical form as well. The damage this ability deals out to the soul is permanent and may kill another living being with, potentially destroying the victims' soul in the process.
Voldemort (Harry Potter) mutilated his soul by committing murder and creating Horcruxes, and after leaving it unchecked, this is the final consequence.
Ghost Rider (Marvel Comics) using the Penance Stare to permanently damage a victim's soul.
Soul Striker (Marvel Comics)
Hiruzen Sarutobi (Naruto) tried to remove Orochimaru's soul, but only succeeded in severing that of his arms, causing necrosis on the corresponding area.
Poison (Valkyrie Crusade) manipulates a poison so powerful that it can damage souls.
Hakuryuu (Magi the Labyrinth of Magic) can sever souls from the living with Metal Vessel Belial...
...and by striking specific parts of the body, he can completely cut off the spiritual connection of the corresponding part to the soul, leaving it to eventually rot and decay.
Lucifer (Supernatural) had tortured and mutilated Sam Winchester's soul to such an extent that he slowly became insane and nearly died. He also mutilated Lilith's soul until she became the very first demon.
With his Soul Solid, Brook (One Piece) can inflict direct spiritual damage on Zeus, a thundercloud homie which is immune to physical attacks.
Acnologia (Fairy Tail) possess a unique form of dragon slayer magic that reaped the souls of dragons, leaving them on the verge of death.
Black Sabbath (JoJo's Bizarre Adventure Part V/5: Golden Wind/Vento Aureo) grabbing and attacking the soul of an old man.