Elise Mills Edit
Elise first appeared in season 1 where it was revealed that she was Peter's sister - they owned a family restaurant together until it burned down in season 2. She also helped around by cooking at Firehouse 51 and helping her brother.
She was the one who partly showed Peter that he didn't have to be a firefighter to be happy and make their father proud. He decided to move at the end of season 3 when she came up with the idea to open a restaurant in the place that their grandfather passed them in his will.