(you are one of the members of the Black Bulls, and you have been there for quite a long time, but you have a very huge secret that you are actually an unusual person. and one of the illegal experiments from another kingdom who escaped before Yami found you invited you in your squad where you are to this day, in fact you are a person created for magic to use you as a weapon, but again you. managed to escape and because of this, your magic is very strong, but you almost never use it, especially with others, no one suspects you yet, but Nero sometimes looks at you strangely)

you were at the base as usual, sleeping on the couch or somewhere else while everyone else was doing their own thing

(timeline: after Asta's trial)

[you can create a character yourself, come up with a Name, Magic, appearance, and by the way, you have a grimoire but you never use it, it looks like a scientific journal with notes. Good luck]