Emerald Sparrow had a dream.
In the dream, she seemed to be living in the past.
In this past, she saw herself as still young, still naive, still proud of being a Magical Girl, and thus answered the Kingdom's call to join the army.
At that time, Emerald Sparrow, or rather Cornflower, was the youngest and most promising Bud Level Magical Girl in the Magic Kingdom. Having just received her word plate certification, she demonstrated her extraordinary abilities during assessments, already making a name for herself among the many Magical Girls.
As such, when the Magic Kingdom went to war with the interworld, even though the Kingdom didn't forcibly require the Material Realm's Magical Girls to participate, and most of the Magical Girls from the Material Realm were unwilling to fight, Cornflower still chose to be the exception, resolutely setting out for the Kingdom.
An Ya, or Ying, went to the Kingdom with her.