Periboia joined the giants in the original attack upon Mount Olympus. She was the only female Giant among them, created specifically to destroy the goddess Aphrodite. She was ultimately overpowered, however, through the combined efforts of Hercules and Aphrodite.
Periboia was among the giants assembled in the Athenian Parthenon, as seen in Piper's dream. She approached her father Porphyrion's throne, and inquired why they have assembled in the Parthenon, rather than the slopes of the original Mount Olympus. The Giant King harshly responded by claiming that the mountain was currently a barren peak that offered them no glory, while the Athenian Parthenon held the Olympians' memory best, with it being the most powerful symbol of the Olympians in the minds of mortals. Porphyrion claimed that when the "blood of Olympus" is spilled there, the Acropolis shall be razed, with the hill crumbling and all of Athens being consumed by an awakened Gaea. Unlike her uncles, however, Periboia wasn't convinced, and tried to dissuade her father from unwisely tempting fate, reminding him of the Seven Heroes of Olympus also having friends in Athens. At Porphyrion's request, Periboia's uncle Enceladus tells her about Delphi being taken back from Apollo (which closed off the future to the Olympians), and introduced his brother Thoon, the bane of the Fates.
Enceladus was able to predict that it would be Percy and Annabeth leading the rest of the Seven in an assault against the giants. Hence, when the Seven Heroes of Olympus finally make it to Athens, Periboia was the one to capture Annabeth, holding her by the neck, like a feral cat. When Annabeth attempts to say something, Periboia promptly shuts the demigoddess up by violently shaking her, and drew her hunting knife, offering to spill "the blood of Olympus". Porphyrion, however, insisted that it must be done by his brother Thoon instead. While Piper did manage to free Percy from Enceladus's grasp, Periboia anticipated the demigoddess' plan, and jabbed at Annabeth with her knife. Annabeth, however, managed to dodge, making the giantess stab her own palm, causing her to drop Annabeth. Annabeth, however, was still wounded, and her blood soaked the earth as she rolled away from the giantess. Piper swiftly pierced Periboia in the gut with her Boread sword, freezing the giantess solid, making her steam white and fall on the ground. Annabeth subsequently retrieved Periboia's knife, but the giantess managed to thaw with alarming speed, and tried to grab Annabeth again. The demigoddess, however, managed to stab Periboia with her own knife, and a deadly game of tag between both of them ensued around Porphyrion's throne. Soon, however, Annabeth began to lose ground against her, but the healed Olympians arrived at that moment, just in time.
Piper ultimately faces off against Periboia, and managed to hold her in a fierce fencing duel. The giantess was ultimately defeated and killed by the combined efforts of Piper and Aphrodite (who floats around them on a cloud and strews numerous rose petals into the giantess's eyes), after which Hades (invisible with his Helm of Darkness) opened up an abyss under the fallen giantess' body, sending Periboia back to Tartarus.
In The Blood of Olympus, Periboia is described as a thirty foot tall giantess, with a bronze breastplate, green dragon-like legs, and long braided hair, much like those of her father and uncles. She is just as tall and burly as her uncles, but Periboia's voice is higher and reedier. She wields a hunting knife that is as long as Piper's sword.
- Prowess in Battle: Periboia is a formidable fighter, able to hold her own against Annabeth and Piper, both of whom are very skilled swordswomen in their own right. However, she is ultimately overpowered and killed by the combined efforts of Aphrodite and Piper.
- Giant Invincibility: As a giantess, Periboia can only be killed by a god and demigod working together, and when she is harmed by anybody else, she heals at an accelerated rate. Hence, she was brought down by the combined efforts of Aphrodite and Piper.
- Periboia is the only female giant.
- Periboia is the only giant who is not a direct child of Gaea.
- According to Homer, Periboia is the daughter of the giant Eurymedon and the mother of Nausithous with Poseidon.