The Book of the Black Bulls is the first Black Clover light novel written by series creator Yuki Tabata and illustrated by Johnny Onda. It was released on August 4, 2016.
The first half takes place shortly after the main storyline begins, in which Asta befriends the runaway Diamond Kingdom commander Fanzell Kruger and becomes his student. They briefly encounter Mariella, a former student who's now working for the kingdom as an assassin and is searching for his missing fiancé, Dominante Code. After telling Fanzell he must find a new reason to live, Asta goes his separate ways.
Five months later, after Asta is injured during his battle with Mars, Fanzell asks the Black Bulls to help search for Dominante while dealing with the Diamond Kingdom's assassination squad.
The Book of the Black Bulls provides examples of:
- Continuity Nod:
- The Magic Knight Entrance Exams are briefly mentioned.
- Dominante Code is originally from the Forest of Witches who left for Fanzell, a man. By the time of Black Clover, the forest is infamous for having an Evil Matriarch who doesn't like men.
- Defector from Decadence:
- Fanzell and Dominante defected from the Diamond Kingdom because they grew dissatisfied with its corruption.
- Mariella quickly becomes a renegade within the Diamond Kingdom's assassination squad as she tells the Black Bulls her plans to destroy the organization. Unfortunately, Galleo decides she has become a liability and fights her.
- Flashback: The anime adapts this story as a series of flashbacks, which occur shortly after the beginning of the Forest of Witches arc and gives greater context on who Fanzell, Dominante and Mariella are.
- Foregone Conclusion: Since this novel occurs before the Forest of Witches arc, anyone who's familiar with the series will know that Dominante and Fanzell have married and Mariella has already joined them.
- Greater-Scope Villain: The Witch Queen casts a shadow on Dominante while
- Heroic BSoD: Fanzell goes through a brief one when Mariella tells him that Dominante might have been killed.
- Karma Houdini: By the end of it all, Mariella joins Fanzell and Dominante after Galleo is defeated. But her job as a Professional Killer involved a lot of criminal activities and she knew that she would face severe punishment had she turned herself in to the Clover Kingdom's Magic Knights. Even so, it will take a serious effort for her to atone for her crimes.
- Let Us Never Speak of This Again: At the end of the story, Yami makes this demand to Gauche after they assist Fanzell in helping the Magic Knights capture the Diamond Kingdom's assassins.
- Origins Episode: The light novel explains how Asta and the Black Bulls befriended Fanzell, Dominante and Mariella.
- Reports of My Death Were Greatly Exaggerated: When Mariella captures Fanzell and Asta in their house, she tells them that Dominante may have already died because the latter's wand was stained with blood. However, it soon turns out that she's alive and well.
- The Woman Behind the Man: Mariella is behind the plot to help the Black Bulls in atoning for her misdeeds as an assassin and avenging her fallen comrades.