The Zoldyck Family's Magical Girl

The original idea wasn't quite enough, so I'm switching to this for now.

I'm a magical girl.

The kind who supposedly embodies love and peace, kindness and justice, wipes out the forces of evil in the world, and protects the happiness of countless families: a magical girl. (Though there are a few differences, it's close enough.)

Now I've run into the worst crisis in history:

I, a genuine, no-false-advertising magical girl, have been reborn in this new world with no magic! (How is that any different from going to the bathroom without bringing toilet paper?)

Even worse, this family is downright inhuman. Every day, someone forcefully holds my head down and brainwashes me over and over:

You're a Zoldyck.

(No, I'm a magical girl.)

You're a professional assassin.

(No, I'm a professional magical girl.)

Getting stronger is your top priority.

(No, staying alive is my top priority!)

A magical girl without magic is like a fish out of water, bread past its expiration date, or a package returned to sender. It could kill me.

And the only source of magic is the power of belief. Believing she's a magical girl works better than any magical elixir or tonic.

This is urgent!

How am I supposed to convince a family of professional assassins that I'm a magical girl who uses magic?

Theme: Everything for the sake of survival