Horcruxes: The Helping hand of Lord Voldermort
Today we'll see the Reconciliation and destruction of horcruxes.
Ron: "Isn't there any way of putting yourself back together?"
Hermione: "Yes, but it would be excruciatingly painful.
"Harry: "Why? How do you do it?"
Hermione: "Remorse. You've got to really feel what you've done. There’s a footnote. Apparently the pain of it can destroy you. I can’t see Voldemort attempting it somehow, can you?
— The trio on reconciling the fragments of a broken soul
The creation of a Horcrux can be reversed by its creator by truly feeling remorse, though the effects of this can apparently be painful to the point of being fatal. However, as described below, this may be a far preferable outcome than the alternative.
Interestingly, since Dumbledore said that "there is no help possible" for Voldemort's soul, it may be that any soul as badly damaged as Voldemort's could no longer be repaired through remorse as described in Secrets of the Darkest Art.
# Alternately, the soul can still be repaired through the redemptive power of repentance. Harry told Voldemort to "try... be a man... try for some remorse. It's your one chance. It's all you've got left." This seems to indicate that though Tom Riddle's soul is maimed and seriously injured, he can still repair it by regretting all the horrible things he did;
# Dumbledore may simply mean that Voldemort is incapable of remorse to save his own soul, or just referring to the fragment that Voldemort himself destroyed and the piece Harry found, as opposed to his "main" soul.
Harry: "So if all of his Horcruxes are destroyed, Voldemort could be killed?
"Dumbledore: "Yes, I think so. Without his Horcruxes, Voldemort will be a mortal man with a maimed and diminished soul."
— Harry and Dumbledore in 1997
Horcruxes can also be destroyed. If a person's body was destroyed, his or her soul would remain intact, whereas with a Horcrux it is the opposite, as the piece of soul depends upon its container to survive. Destruction of a Horcrux is difficult, but not impossible, and requires that the receptacle to be damaged completely beyond physical or magical repair. When a Horcrux is damaged to this point, it may appear to "bleed" (ink in the case of Tom Riddle's Diary and a "dark blood-like substance" in the case of Ravenclaw's Diadem) and a scream may be heard as the soul fragment perishes. However, as a safety measure to protect one's immortality and precious soul fragment, the creator would usually place powerful enchantments onto the artefact to prevent damage, to the point where the most powerful house-elf magic will not succeed.
# It is unknown if the creator of the Horcrux would be able to sense that his soul fragment was destroyed, although Dumbledore stated that in the particular case of Voldemort, he wouldn't feel their loss because his soul was sliced too many times and stayed that way for too long.
#All known methods of Horcrux destruction are as deadly as the murder needed for its creation. For example, the earliest known method is administering basilisk venom to the Horcrux, the only cure for which is phoenix tears, an extremely rare substance. Other known methods are Fiendfyre (as evidenced by its destruction of Rowena Ravenclaw's Diadem), which requires extreme skill to control and the Killing Curse which seems to be capable of destroying a Horcrux if it is animate, given that part of Voldemort's soul contained in Harry Potter was destroyed when he was struck with the Killing Curse in 1998.However, Harry Potter was never an intentional Horcrux and so it may not work on a proper, animate Horcrux (like Nagini), probably having unforeseen side effects.
#Harry Potter was not destroyed as a Horcrux in the Chamber of Secrets because Fawkes' tears saved him and hence the "receptacle" (Harry) was not then destroyed beyond repair.
# Albus Dumbledore, Ron Weasley, and Neville Longbottom used Godric Gryffindor's Sword to destroy Marvolo Gaunt's Ring, Salazar Slytherin's Locket, and Nagini respectively. This was only achievable as the sword is a Goblin-made artefact, which can absorb qualities that strengthen it. When Harry Potter slew the Basilisk in the Chamber of Secrets, the sword was imbued with Basilisk venom and became capable of destroying Horcruxes, as Basilisk venom by itself is destructive enough a substance to destroy a Horcrux.
Harry Potter and Hermione Granger used Basilisk fangs from the Chamber of Secrets to destroy Tom Riddle's Diary and Helga Hufflepuff's Cup, respectively.