Sassho-seki Stone

The Sassho-seki stones are ovoid and smooth egg-like grey rocks with orange marble patterns across the surface. It shines when under a light source, like something alive is inside of it.
They are fragments of the essence of the Great Demon Tamamo herself, and were used in the past to convert mortals into Oni by giving them powers in form of a Blight. After Tamamo was defeated in battle by Kumiho, her body was banished in the deepest Abyss, being destroyed in the process. The Sassho-seki were created once more and gathered power in the dark.
Shuten-Doji, King of the Oni, has taken great care of cultivating the Stones, and now sends them along his agents to the Prime Material to corrupt the mortals again, allowing Tamamo to regain the strength he lost during the World's Breach.

Mechanics & Inner Workings

The Sassho-seki stones can be used either in rituals or by a willing individual who knows what it is. Either way, the victim is infected with Yokai Blight, and gain access to powers it didn't have before.

In game mechanics, it works as follow :
When you use the spell "Identify" on the stone, you must succeed on a DC 15 Wisdom Saving Throw or the spell has no effect. If you fail, you can't use your "Identify" spell for 1d4 weeks, the spell backfiring and giving you an ill feeling. The DC for successfully identify the stone drops by 1 point for the next time but can't be less than 12.
You can try to use the stone on yourself with an action, sinking it into your chest. You must succeed on a DC 13 Wisdom Saving Throw or not being able to inflict such pain upon yourself. If you succeed, you take 2d6 necrotic damage and gain the following benefits :
You roll Xd10 Hit points, X being half your character level, round down. You must make a DC 15 Constitution Saving Throw. On a success, those hit points aren't temporary and raise your maximum Hit points permanently. If you fail, your maximum Hit points drop permanently. They can't be restored. Whether you fail or succeed, you gain resistance to necrotic damage permanently.
Once you use a Sassho-seki stone, it's power is drained in you and it become a simple rock with no magical properties.

Manufacturing process

The Sassho-seki stones are created from the essence of Tamamo by mystical means.

Item type

Religious / Ritualistic

Related Condition

Yokai Blight

Rarity

Very rare.

Weight

2 kg

Dimensions

30x15 cm