Kagedama

Description
The Kagedama (影魂, lit. Silhouette Spirit) is a mushi that resembles a translucent snake-like shadow. It resides in the shadows of old trees. When animals and people rest in the tree's shade, it enters through the ear of its chosen host and embeds itself in the brain. There it begins to consume memories, apparently in no particular order, though memories necessary for the host to function are likely left until last in order to prolong the host's lifespan. In addition, the host is inflicted with insomnia except for very brief moments when the Kagedama splits itself and sends its offspring out of the host to take up residence in the shade of a nearby tree. Sufferers also rarely sleep, but prefer to work day and night without rest.

Weakness
The Kagedama is vulnerable when exposed to sunlight. However, once the mushi has embedded itself in a living host, it cannot be removed, though its effects can be delayed by focusing on those memories that the sufferer does not want to lose, such as memories of loved ones, or of daily tasks.