Big Sis Context here is more of in the line of slang of respecting another female.

The hell you think you're doing!

The enemy are drawing away...!

She's letting it all out?

If I show my true self to my allies, then the men of the upper class will stay far away from me..I can't let that happen!

Eek! I'm so scared! Help me!

You place your hands on my comrades! You will not leave with your life!

I will beat you black and blue!

I want to call her "Big Sis"!