Crossed Hearts

Crossed Hearts also known as the Beating of Linked Souls is a sacred gear that is possessed by a member of the Rebirth Organization. Originally viewed as a useless sacred gear to supernatural forces that was only fit as a gift for the human world, due to the meddling of a certain witch, it became a mid-tier sacred gear.

Summary
The first wielder of this sacred gear was a stone mason from a ancient civilization, however he unintentionally passed this sacred gear to his son who became a decent accomplished soldier. It was then in his death passed this sacred gear along to a dog of his village who later bit a young girl, thus giving her the sacred gear. This continued for many centuries until this sacred gear unintentionally fell into the hands of a witch in Japan around the 10th century. After learning she was set up by the devils who was using a war to get rid of her kind she angrily shouted spells and curses at the devils and thus triggered a chain of events that mutated this sacred gear.

Before the devil could realize what he had done, he killed the witch and a few days later he was afflicted with a power curse that caused him to commit suicide by setting himself on fire.

Abilities
The original abilities of this sacred gear is that it allows someone to gain the wisdom and experience of the previous wielders. This can allow them at times to see flashbacks and experiences that the previous owner saw, making them more wiser, and intelligence. This has been the reason that so many individuals were accomplished military generals or warlords. It was later stated that legendary individuals like Julius Ceaser managed to obtain this sacred gear.

Witch's Curse
Considered the sub-species and only balance breaker of this sacred gear. The witch's wrath and anger causes individuals to gain immense strength, speed, and a deadly aura that allows them to fight on par to the individual they are facing. Due to the young witch's wrath specifically aimed at devils the sacred gear is known to cause wielders to feel anger and wrath when facing against devils specifically. The current wielder states that when he first met Simon it was as if his blood itself was telling him to rip Simon's head off.

Lifeless
A curse unintentionally imbued in the sacred gear, if a supernatural creature kills the wielder it will cause them to gain horrible and lifelike hallucinations that will play on their guilty conscience and eventually drive them to suicide or drive them to kill others thus playing even more on their guilty consciences. Niklaus later states that his hallucinations never stopped and it was only due to him living for so long that they eventually disappeared.

Drawback
It was stated that only pure-blooded humans can inherit the sacred gear, known to be one of the few of it's kind with this type of system in place. While the wielder can fight on par to a individual supernatural creature in regards to speed and strength, magic, multiple enemies, and individual skill still poses a danger to them. Due to the wielder feeling such anger and wrath towards devils this could cause them to act impulsively leading to their death.

Trivia

 * All for One from My Hero Academia was inspiration for this sacred gear.