The jacket isn’t even theirs. It belongs to some humans that her brother has taken an interest in, enough that he is willing to throw himself into their fight.
She fights alongside him. Not because she cares about the humans or understands his motive, but because they always support each other, no matter what.
The difficult part isn’t the fight, but tempering her strength. Humans are fragile, and even the strongest human among the group is like a house fire to her and her brother’s blazing firestorm. She fights with light touches and swipes from afar, but as much as possible, she leaves the humans to fight among themselves.
Her brother’s humans see the gap in strength between them and wants to be stronger, so she spars with them. She is as gentle as you can possibly be, but even that leaves the humans exhausted.
She doesn’t understand why her brother wastes his time on these humans. They are weak, care too much about the unimportant things, and will be gone in the blink of an eye. Why waste their time with them?
Then one of them knocks her staff out of her hand.
She has been gentle with them, but it’s still an achievement. The humans continue their sparring session with renewed strength, and she allows herself to be a little less gentle.
Little by little, she unveils more of her strength, and the humans chase after her and her brother with everything they have, until the day comes when she actually needs to make an effort as she spars.
It is great progress in a short period of time, and she watches the delight in her brother’s face as his humans continue to grow.
She thinks she might know why he’s putting everything on the line for them.