About becoming a magical girl

[Micro-depressed, Bianbai 1v1, Micro-knife has sugar]
She is an agent and an idol. She used to be a "brother", but now she can only disguise herself as a man, struggling to maintain her last dignity as an elder brother.
Until...she saw her younger sister standing in front of her holding an exaggerated support sign with stars in her eyes.
She was dumbfounded.
I'm your brother!