Krone

Sister krone or krone was a sister/helper in the promised neverland and helped run the grace field house orphanage with madam isabella. She possessed a large and intimidating physique, which coupled with her equally intimidating facial expressions made her seem dominant, though she outwardly often wore a bright, warm smile.

Krone was an individual who fought for nothing but her own, personal, agenda. She played nice when she had to play nice, scheming and plotting continuously while trusting no one but herself. She fully realized the evil of her own actions, and how the twisted system she was brought up in made her this way, but still carried on nevertheless. Her goal was ultimately just to survive, to be on the "Eat" part of the food chain.

She was brought up in an "Orphanage" similar to the grace field house and performed well enough on the tests to be recommended for mama-training when she turned 12. Krone was very intelligent, having obtained perfect scores on the daily tests during her own time in an "Orphanage". However, she was still inferior to isabella and fell short in her attempts to outwit her as she tried to usurp isabella's position as "Mama" of the orphanage. Nevertheless, she continued her attempts to obtain an advantage so that she can "Drag her down" from her position.

Trivia:
Her name "Krone" is the german word for "Crown", which fits with her desire to usurp isabella's position as a mama.
Krone left a pen she got and hid it somewhere in the house.