"Bella"

As Derek becomes more and more social and more and more verbal, his people preferences emerge. He seems to be a "people person" with many favorites, but few can compare to "Bella" (aka Gabriella Kimsey). Perhaps it's because she takes him out of the "3rd wheel" roll with Drew and Gabriella's older brother Judah, but Derek can sit and watch and talk to Gabriella for long stretches of time.