Brigid's diary

Brigid's diary is a magical book created by the Celtic goddess Brigid as a gift to humans.

History
In ancient times, Brigid created a magical diary as a gift to humans.

At some point in the past, the diary was sealed in Mallus's realm along with other magical creatures.

Disturbance in Tokyo Bay
After the Legends freed Mallus from his realm to defeat him, the diary and a multitude of magical creatures were spread throughout the timeline.

The diary was displaced in 1951 Tokyo, Japan, where it found its way to a film director, Ishirō Honda, who created the fictional creature Tagumo in his imagination as a representation of the destruction caused by the bombs dropped on his home, Hiroshima during World War II. Once Ishirō took possession of the book, the diary itself drew Tagumo's storyline from Ishirō's imagination. In the diary, Tagumo's story ends with the octopus destroying Tokyo.

After Ishirō was confronted by Zari and Mick on the recent unusual marine activity, he tried to throw the diary in Tokyo Bay to try to erase Tagumo from existence, only for the book to find its way back to Ishirō. Charlie then goes to explain that the book bonds itself to artists with creative minds, and that Tagumo won't cease to exist until its story is played out in full.

Ishirō attempts to create a new ending to Tagumo's story, only for his pen's ink to be erased as soon as he draws on the book. Charlie also explains that the book was created to help artists express themselves, and that he can't create a happy ending as he didn't have a happy life.

Mick then bonded with the diary and wrote to bring Garima, a character in his original story, to life to battle Tagumo. The story ended with Garima vanquishing Tagumo and making passionate love with Buck (pertaining to Mick). The Legends return to the Waverider where John Constantine keeps it in his chest of his possessions.

Confiscated
Sara and Ava, to her surprise, see Garima on the Waverider, to which Ava argues that letting Mick use the diary is dangerous. This lead to Ava to confiscate the diary as a safety precaution. She then declares that the book is officially Time Bureau property.

Powers

 * Magical bond: The diary is attracted to a person with a creative mind (e.g. artist, writer, etc.) and bonds with them, physically and empathically.
 * Fiction manifestation: When the diary is bonded to an artist, it brings any story from their imagination into existence until the story ends. Other artists can interfere with the story by also bonding with the book.
 * Enhanced creativity: The diary boosts the creativity of whoever it is bonded to.