Your character has formed a bond with a Shikigami which allows them to fuse into one being. When the character and Shikigami are fused, the character gains free tranformed dots with a value in Experiences equal to twice his dots in this Merit, within his trait caps. Also, if the character lacks a pool of Wisps, fusion supplies one that holds Wisps equal to his Resolve + Presence. However, the Shikigami cannot take actions while fused - he shares the character’s senses and may mentally speak to him, but the integrated body is controlled by the character.
Fusing with a Shikigami is quite similar to a Noble’s transformation, and uses almost the same rules. It takes an instant action to fuse and the Shikigami must be touching the character; the player does not roll. The Shikigami maintains the fusion, so the player rolls twice his dots in the Merit to sustain a fusion past a scene’s end. Dramatic failure on this roll leaves the Shikigami exhausted, and blocks use of the Merit until he has spent a full scene or an hour resting. During a fusion, the character’s clothes, body or both gain aspects of the Shikigami’s appearance that disguise him, giving the character the protection of Dual Identity.
While the benefits above are automatic, the Shikigami can cultivate the bond to let his partner draw on the Light deliberately. The character may learn Charms with an effective rating up to his dots in Unison, paying Experiences equal to that rating. He may also buy 1 Invocation dot for each dot in Unison, if he otherwise lacks that ability. However, he may use these Charms and Invocations only while fused with the Shikigami - they are really the Shikigami’s powers, that require a human partner to activate. If the character permanently loses his partner, the Experiences spent on Charms and Invocations are refunded under the Sanctity of Merits.