Resembling a cross between a rabbit and a squirrel, he first encountered Samus, who was at the time only 3 years old, in the woods of Planetary Colony K-2L and snatched her backpack. He was eventually chased up a tree, where he refused to leave. Samus and "Bird Grandpa" managed to get him down after the Chozo suggested that she calm down and give it a name in order to see if it wanted to be friends, and thus Pyonchi was aquainted with Samus.
After the Space Pirate attack, Samus brought along Pyonchi with her to Zebes. Years have passed since then, and Pyonchi still appears to be in good shape and has not yet shown signs of old age, so the lifespan of his species is of yet unknown. He usually stays around Samus out of years of trust, and both treat each other very well. Pyonchi appears to have at least some sentience based upon his actions and wide range of emotions shown so far within the manga. He also gets along well with the prototype larval Metroid.
Years later, it later detects a Mimic during an assassination attempt on Chairman Keaton. Samus brings him to the Galactic Federation Academy when she, Chairman Keaton, and Adam Malkovich go to the Academy's research facility. Pyonchi mauls a student who was insulting Damara and her friends. Samus, before she leaves the Academy, sees Pyonchi playing with them. She smiles, and leaves Pyonchi there while she goes on her Zero Mission.
- Samus's pairing with Pikachu in the Subspace Emissary mode of Super Smash Bros. Brawl may be a reference to Pyonchi, since the Zero Suit's first appearance was in the manga. Her reaction to Pikachu's pain might have been in remembrance to her friend.
- Pyonchi is yet another example of a similarity to the Alien film franchise. Pyonchi serves the same role as Jones/Jonesy the cat, being the pet of the main character. Both Pyonchi and Jones survive the K-2L attack/destruction of the Nostromo, and are left in the care of someone else as their owners go on different missions. What becomes of them afterwards is also unknown.