She is just a girl with memories of her 'past life'.
She exists in an organization called 'Nursery Rhymes', where men are 'princes', 'knights' or leaders - 'kings', and women are 'princess' or leaders - 'queen'.
Everyone who calls themselves a princess is a Mary Sue!
She clearly thought that she was not a Mary Sue, but unexpectedly discovered that she was really a Mary Sue.
"Her Royal Highness Princess Rose, you are the candidate for the leader of 'Nursery Rhyme', and you must bear the responsibility for this."
"... Please call me queen."
…
What happened to me
I promised to let it go
why at this moment
Corners of eyes become warm
Washed away the foam
tattoos in bloom
It is still graceful
My heart withers
do you still love
Love this red
like me once
bloomed for you
…
Intention: