Pepe the child gibbon lives in a rural area with her mother (though she tells the humans she was living with her aunt, as her mother had died when she was young). At some point her mother had become caught in a trap and been rescued by Gôdo, which led to Pepe becoming his friend. When the escaped humans from another time saw Pepe's home, they hid inside, scaring away Pepe's mother but making a friend in Pepe. After the humans flee to Gôdo's Green Mountain hideout, Pepe follows them to warn that Gebâ has set fire to the mountain. She later pleads for the life of the humans when they are set to be executed by Gebâ and the villagers.
After the humans are taken to the ape city headquarters, Pepe, who had stowed away in the truck, manages to break in and frees first Jirô and then Gôdo. They escape before returning to rescue Kazuko and Yurika. They make a long escape from the city and eventually Pepe is returned to her grateful mother by Gôdo, before they travel back to Green Mountain without her.
As the only ape friend to the fugitive humans she fills a similar role to Galen in the Apes TV series being made around the same time in the US.
