Weapon (odachi), artifact (tsukumogami, requires attunement)
Omen: When the sword is first drawn by a creature it kills that creature outright. This only happens once and if the creature somehow returns from the dead, they automatically attune the sword and can then wield it normally
Deathblow Omen. When used to slay an immortal creature the wielder gets a glimpse of the creatures life as a human and the exact steps and conditions that lead to it becoming a monster.
You gain a +1 bonus to attack and damage rolls made with this greatsword. Fushigiri glows with red light, shedding bright light for 20 feet and dim light for an extra 20 feet in the presence of immortal creatures. Once per day, the wielder can cause the sword to flash a baleful, blinding red light. Immortal creatures within 30 feet must succeed on a DC 15 Constitution saving throw or be blinded for 1 round.
Against immortal creatures it is a +4 magical weapon and if used to deliver the killing blow to such a creature it permanently kills them.
The wielder may use a Reaction to slay an oni as it discoperates.
Not many know that Fushigiri – The Mortal Blade also has another name – the Demon King’s Sword. Though not an evil weapon its abilities have earned it this moniker. Even fewer people know it’s the same weapon. Once successfully attuned and used to slay an oni it gains the following traits:
- Sentience. Fushigiri is a sentient lawful neutral weapon with an Intelligence of 17, a Wisdom of 10, and a Charisma of 19. It has hearing and darkvision out to a range of 120 feet. The weapon can speak, read, and understand Common, and can communicate with its wielder telepathically. Its voice is deep and echoing. While you are attuned to it, Fushigiri also understands every language you know.
- Purpose. To slay oni and make sure the Golden Contract is enforced. It recognises oni on site and can communicate as much to its wielder.
- Yokai Shift. Whenever it kills an Oni hand the PC the monster statblock. The PC may now pick one ability from the oni’s list of actions and they become class abilities for the PC. They may use this trait once per day and when the character has more than one yokai shift option they may switch options during a short rest.
- Omen III. When the PC uses aspect of the oni it momentarily appears as the oni the trait was taken from.
- Yokai Shift I. You may have 1 oni trait active.
- Yokai Shift II. You may learn 2 oni traits and use each once per day each.
- Great Weapon. You have reach (10 feet) while wielding Fushigiri.
- Crashing Waves. If you move at least 10 feet towards a target in a straight line you have advantage on the attack roll.
- Yokai Shift III. You may learn 3 oni traits and use each once per day each.
- Dawn’s Light. If you are ever knocked prone you may make an attack against a target within reach as part of your move action.
Tsukumogami were man-made items of exceptional quality that had had their kami awakened, either through the skill used in creating them or through their association with great deeds. These items can usually only be attuned or used by a single person. They grow in power as the hero who owns it also grows in fame, honour and power.
*What is an immortal creature? Anything that doesn’t die permanently when killed (demons, devils, vampires and so on), but specifically, for this campaign, it is oni.