Seishinbuki

Seishinbuki (精神の武器, Spirit Weapon) are weapons with spirits inside them. Spirits of dead ninja/samurai travel into the ninja's weapon, enchanting it. The weapon that the spirit travels into gains the powers of the ninja/samurai the spirit is from.

Example: If the First Hokage's Spirit traveled into a ninja's weapon, their weapon would gain wood powers.

Seishinbuki also have unleashed forms. If your weapon turns into a Seishinbuki, it would gain the ability to unleash it's power and turn into a different form. The user of the Seishinbuki cannot use the powers until they unleash it.

Unleashing a Seishinbuki is not an ability the user gains automatically. The user must first connect to the spirit and communicate with it. Learning who they are, actually meeting them, and becoming close friends.

They connect to it by meditating. Whether in their sleep, close to dying, knocked out, or sitting in a quiet place. That is how the user connects with it. The weapon must be held in both of their hands too.

Once the user learns who's spirit is in the Seishinbuki, they will be able to unleash the power. But that's only the beginning of it. They are only able to unleash to a certain extent. This extent is called Shoki Kaihō (最初のリリース, Initial Release).

The Shoki Kaihou is the second form of a Seishinbuki and allows the weapon to change shape and gain special abilities. The shape changing can include the size, texture, and any other physical qualities and appearance of the weapon. The abilities are the abilities of the spirit in your Seishinbuki. So your spirit can't be the First Hokage, and then your Seishinbuki has the abilities of shadows.

The Seishinbuki is released by saying an incantation. Any incantation is fine, but their must be a contract between the spirit and the user agreeing on that incantation. The incantation must be said, then the spirit's name.

Example of Shoki Kaihou
Incantation: Exterminate evil, with the growth of wood. Hashirama Senju.
Appearance: The sword transforms into a sharp, smooth wooden sword.
Abilities: The ability to make wood grow from the surface.

That is just a short example. The real thing would of course have more description and more quality. Seishinbukis also have another unleash form. It's called Kesshō Kaihō (最終リリース, Final Release).

The Kesshou Kaihou is the final form of a Seishinbuki. Instead of the weapon transforming, the user must materialize their spirit and bring it into the physical world. The change in power are 5 to 10 times bigger than a Shoki Kaihou.

To unleash a Kesshou Kaihou, the user must say "Kesshou Kaihou." The abilities of a Kesshou Kaihou are enhancements of the Shoki Kaihou. Way bigger enhancements because while Shoki Kaihou transforms, Kesshou Kaihou materializes.

Example of Kesshou Kaihou
Appearance: Huge Wooden Dragon
Abilities: The wooden dragon is under the user's control and can manipulate wood, transform into various wooden shapes, and create large wooden structures from the ground.

See the big difference. While the Shoki Kaihou transformed into wooden sword, the Kesshou Kaihou materialized into a dragon.