Overeater

Overeater (喰らい尽くすもの) is a demonblade currently in the possession of William. It was originally owned by the High King.

The Boy in the City of the Dead
The demonblade, Overeater, was given to William as proof of his independence by Blood after their final duel against each other. It was one of the strongest demonblades in his possession and was originally owned by the High King.

The weapon can cut down anybody, including echoes, as long as the blade reaches them, the blade is inscribed with many words too difficult to figure out, however, it's effects are able to be described in one sentence...

"As you cut living being with this sword, it recovers your life force. The more you cut, the more you recover."

William was warned by Blood, not to rely on this weapon, as he would grow too independent on the weapon, he takes his words to heart and tries his best to only use the weapon when required.

The first instant, William has used the demonblade was against the splinter of an echo, the god of undeath, Stagnate. He was able to cut through his body multiple using the weapon.

The Archer of Beat Woods
The second instant, was against an ambush of wild animals and serpents lead by a Chimera. He lost control of his emotions after witnessing his closet friend, Meneldor, take a heavy blow against the Chimera, filled with angry and hatred he slaughtered the animals and serpents without any real strategy or grace, making him feel like a failure in the eyes of what his foster family has taught him.

The Lord of the Rust Mountains
The third and final instant, was when he took an direct and final attack, consumed by miasma and scorching heat from the vile dragon, Valacirca. His body was not able to withstand the intense heat and poison and started to melt, before losing consciousness and ready to accept his fate, he heard the voice of Mary, determined to live, he pulled out Overeater and slashed repetitively at the dragon, regenerating and melting constantly until he lost consciousness.

Ability
Life steal : The Demonblade able to absorb any matter of life force allowing the user to drain it's enemy in order to heal themselves.

All Thing Slayer : The Demonblade can be used to cut everything including Echoes and the sharpness itself cannot be unmatched by any kind of blades making it the most powerful weapon.

Bloodthirst : The Demonblade possessed ability that can manipulate the user to use the blade to the fullest albeit forcing the user to be dependent on it and severing any kind of concern to the others allowing the blade to fulfill it's thirst of blood of the enemy by gauging the user desire to cut everything and destroy everything.