Pewku was a retired Ussal racing crab who befriended Takua. In Metru Nui she pulled an Ussal cart driven by Orkahm. After migrating to Mata Nui, she was a racing crab and later a means of transport for Matoran traveling between Onu-Koro and Po-Koro. She was Takua's companion during the search for the Seventh Toa. She was then adopted by Jaller. After Jaller's departure from Metru Nui, she befriended Kapura, although she was not adopted by a new owner.
Takua the Chronicler rode his Ussal crab, Pewku, on the search for the Seventh Toa.
Pewku was a crablike Ussal. She was Takua's faithful pet.
On Metru Nui, Pewku [sic] was Orkahm's favorite Ussal crab, the one he had been riding for as long as Matau could remember.
Orkahm spent many years with Pewku as his Ussal crab. Later, Toa Hordika Whenua seemed to take a liking to her, going so far as to suggest that the Toa take her with them when they leave Metru Nui.
Pewku likely remembered her time in Metru Nui.
Pewku changed forms because she grew older. Ussal crabs changed as they grew.
Pewku's later appearance was a different shape and much larger as a result of her evolving.