The Demon Sword Lostvayne「魔剣 ロストヴェイン Maken Rosutovein」is a sacred treasure belonging to the Dragon's Sin of Wrath, Meliodas.
Lostvayne is a weapon that takes on a form of a curved shortsword with the Dragon tattoo emblem into it and has five holes on the sharp blade.
Lostvayne was entrusted to Meliodas by King Baltra, and was in Meliodas' possession until 10 years ago when he sold it in order to raise money to open the Boar Hat. Merlin later bought it from a pawn shop in Camelot and kept hold of it until she returned it to Meliodas during Albion's attack on Camelot.
While saving Arthur from Albion's attack, Meliodas' sword which was a gift from Liz is broken, leaving him without a weapon. This prompts Merlin to return Lostvayne to him in order to combat the giant monster.
By saying the command "Sacred Treasure Activate"「
- Jitsuzō Bunshin「
実像分身literally meaning "Physical Clone"」: The sacred treasure Lostvayne's special ability that allows Meliodas to create up to four clones of himself.  The clones only retain a fraction of the original's power, with one clone having half the power level of the original. The halved power level is divided among each additional clone. Each Physical Clone is still able to use Full Counter to its full potential as the attack focuses on the enemy's attack power rather than the one using Full Counter, this allows Meliodas to use Full Counter multiple times on the same attack. Depending on the enemy and Meliodas's power level, it is additionally possible for him to use his clones to fight the enemy, dealing and taking damage without Meliodas himself getting involved in the fray.
- Lostvayne is the fourth Sacred Treasure to be revealed in the series.
- Lostvayne was worth a thousand gold pieces when Meliodas sold it in a market in Camelot.