Overeater

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

The Boy and the City of the Dead
The demonblade was given to William as proof of his independence by Blood after their final duel against each other. It was noted to be one of the strongest demonblades in his possession which 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 used the demonblade was against the splinter of an echo, god of undeath, Stagnate. He was able to cut through his body multiple times using the weapon.

The Archer of Beat Woods
The second instant, was against a ambush of wild animals and serpents lead by a demon. He lost control of his emotion after he witnessed his closet friend, Meneldor, take a heavy blow against the Chimera, he ended up slaughtering all the animals and serpents without any strategy or grace.

The Lord of the Rust Mountains
The final instant, was when he took a 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 started slashing at the dragon, regenerating and melting constantly until he lost consciousness.