Masamune is a magic weapon that can take the form of a living entity of the same name.
Masamune is a traditional Katana with a solid black blade and matching black hilt said to be stained by darkness. It is legendary for being an evil sword that slowly consumes the soul of its user after taking control of their body, after consuming the users soul the blade absorbs their strength and becomes stronger. It is also said to have the ability to manipulate Shadow Magic. The souls of those unfortunate people are trapped within the swords own seperate world like that of the celestial spirit world.
The swords physical power is great as it is described to be heavy with the souls of its victims and can crush buildings with its immense strength. Combined with the ability to use shadow magic the sword can increase it's crushing strength by covering itself in a puppet like shadow.