Den (デン) is the Rockbell family pet. It is apparent that she lost her front left leg by unknown means prior to the start of the series, as she wears an automail limb in its place.
Den is fiercely loyal and, as such, has been called "Resembool's best bodyguard" by Pinako. Den is also particularly compassionate as shown by the way she attempts to comfort Pinako after Winry leaves home to work at Atelier Garfiel in Rush Valley. Edward Elric once mentioned that Den ate Alphonse Elric's cake, making Al sad. Unfortunately, Den is put largely on edge by Van Hohenheim's strange aura when he arrives at Pinako's house and nearly has to be restrained from attacking him.
In the last chapter, even she is surprised to see Al had regained his body, barking excitedly at the sight of Ed and Al. In a gaiden, she takes Al's helmet so for a family of baby birds.
- Arakawa has revealed in some story notes that Den's name originated from a dog she herself once had, a male dog named Densuke. The name is actually a Japanese variety of watermelon, considered to be the most expensive (and tasty) in the world.
- Den's gender is actually male in the English dub performed by the Funimation in all animated media.
- Fullmetal Alchemist Perfect Guide Book #2; First printed in September 2005; Square Enix; Japan
- Fullmetal Alchemist: Brotherhood, Episode 64: Journey's End;