A pithos is a large ceramic jar used by certain ancient civilizations that bordered the Mediterranean during the Neolithic, the Bronze Age and the Iron Age. It was primarily used to store liquids, such as wine and oil, or food, such as grain. Some pithoi were also used for rituals and burials.
According to the ancient Greek poet Hesiod's Theogony, Pandora's box was originally a large jar, a pithos. The shift in object is attributed with the 16th-century humanist Erasmus of Rotterdam, who erroneously mistook the Greek pithos (storage jar) as the Greek pyxis (small box) when he translated Hesiod's original story into Latin.
In Greek mythology, Pandora's box is said to have contained all the evils of mankind, such as death and disease. Pandora, or her husband Epimetheus in some variants, opened the box and released all the evils, except for one, into the world. The one item that did not escape and remained within the box was hope which in some depictions was treated as the worst evil of all.
"A set of mysterious objects Sophia uses in battle to mimic the powers of Persona-users. Though they function similarly to Personas, their inner workings are completely unknown. It’s name is derived from the Greek word for "jar.""
—Persona 5 Strikers background
Sophia summons Pithos to fight Shadows alongside the Phantom Thieves, in an attempt to mimic how a Persona functions. It specializes in Bless skills, as well as healing and defense debuff.
Later, in order to render herself immune from her misguided creator Kuon Ichinose's attempted brainwashing and attempts to reform her, Sophia receives an awakening, turning Pithos into its true form, Pandora. Pandora is awakened exactly like any other Persona (migraines, followed by the user ripping their mask in severe pain) and grants Sophia newfound strength, giving her the ability to learn the skill Makougaon. The only other Persona that naturally learns this skill is the post-game Persona Metatron.
Pithos represents Ichinose's discarding of Sophia, after she asked her what a heart is. Pithos represents the "hope" Ichinose trapped after shutting Sophia down and giving Madicce the Artificial Intelligence EMMA instead, an AI which has no comprehension of the human heart and operates merely on logic.
Similar to Aigis, another artificially created entity, Pithos is similar to Palladion in the sense that it does not represent a Mythlogical figure, but instead an item related to that figure, and later awakening to that figure as a Persona, with Pallas Athena and Pandora specifically.
Pithos is the first player-controlled entity in the series to lack an Arcana, though races and inexistent Arcana have featured in earlier titles.
All of Pithos' skills have a question mark behind it, representing how it is not actually a Persona and how its skills are perhaps only mimicking what a Persona does. (For example, "Dia?," "Kouga?" etc.) They are removed when it awakens into Pandora.
In Strikers's initial storyboard, Pithos is labeled as "Funnel," a reference to fictional Newtype weapons used in the Mobile Suit Gundam anime franchise that are similar in shape and motion to Pithos' form.