The Street Fighter X Tekken prologue comic book reveals that it was created by Capcom character Ingrid as a 'gift' for Earth, and to test humanity by using the temptation of the box's power. The object crash-lands in Antarctica, and subsequently gains major media attention after its discovery. Studies on the object have revealed, however, that it appears to draw power from conflict, during which it releases a powerful energy.
Researchers fittingly name it Pandora after the Greek mythological figure and the conflict she unwittingly created by opening a box given to her by the gods. The object has also drawn the attention of many fighters from the Street Fighter and Tekken universes, whose motivations are explained below.
- Ryu, after being told of the box by Chun-Li, searches for Pandora in the belief that it has some connection to the Satsui no Hado. Ken Masters joins him, acting out of concern for his friend.
- Guile is sent by his superiors to investigate Pandora. Abel learns that Shadaloo is also seeking it, so he teams up with Guile in the hope that he'll learn more about who he is.
- After discovering that both Shadaloo and the Mishima Zaibatsu are heading to Antarctica, Chun-Li follows to investigate their movements, inviting Cammy White to accompany her.
- Dhalsim heads to Antarctica after several children in his village disappear. Sagat joins him, hoping to find a young girl from his village who also went missing.
- Poison and Hugo Andore learn that the media have gathered in Antarctica, so they decide to travel there to "show off their assets".
- Learning about Pandora from a subordinate, Rolento F. Schugerg plans to destroy it in order to prove how strong his army is. He seeks assistance from the elders of Ibuki's village, who force her to assist him.
- Zangief seeks Pandora to prove his loyalty to Russia. He asks Rufus to assist him in his journey; Rufus wants to get rid of Pandora after its media attention overshadowed that of his victory at the North American Martial Arts tournament.
- Under orders by M. Bison from Shadaloo, Vega and Balrog head to Antartica to obtain Pandora, despite their mutual dislike for each other.
- After Shadaloo received word of the mysterious box, Pandora, which rejected Psycho Power from Shadaloo's satelite, M. Bison decided to head towards Antarctica to secure the box, and requests the assistance of Juri Han, one of his underlings who had lost her left eye and her parents to Shadaloo.
- Akuma hears a voice that is loud and clear just as the mysterious box, Pandora, within the meteorite enters Earth's atmosphere. He decides to head toward Antarctica to find the origin of the voice where Pandora landed.
- Blanka heads to the South Pole after his friend, Dan Hibiki, goes missing months after his journey to Pandora. Sakura Kasugano, interested in the box and wanting to go on her first snowy vacation, accompanies him.
- Guy learns of Pandora and seeks to rid the world of it. He unexpectedly runs into long time friend Cody Travers and asks for his help. Since his hometown is boring, Cody accepts.
- Elena is summoned by a tree in Dudley's garden. The tree tells her that she and Dudley must travel to the South Pole. While Dudley agrees to go, he is aware of, but uninterested in Pandora.
- Kazuya Mishima plans to acquire the power of Pandora in order to strengthen his inner devil power and wrest control of the Mishima Zaibatsu from his son Jin. He is joined unexpectedly by Nina Williams, who had previously tried to kill him, but now seems to want to assist him.
- King II learns that a man resembling Armor King I, long-since killed by Craig Marduk, has boarded a ship to Antarctica. After Marduk also learns about this, the two team up and begin an uncertain trip to the South Pole.
- Julia Chang learns about Pandora's power and, worried that it could easily be used for evil, hires Bob Richards to assist her in finding it.
- In their search for Pandora, Shadaloo and the Mishima Zaibatsu come into conflict and end up destroying the grounds for a mixed martial arts tournament. Hwoarang and Steve Fox, who were fighting each other at the time, form a temporary alliance to exact revenge on the two companies for interrupting their battle.
- Yoshimitsu discovers that his sword is resonating, and believes it has something to do with the mass of fighters heading to Antarctica. He encounters Raven, who is also investigating the issue. Although he does not trust Yoshimitsu, he agrees to work with him under the condition that he takes lead.
- Heihachi Mishima learns that both Kazuya and Jin are heading to Antarctica to seek Pandora. He decides to head out there himself in order to kill them, take the box's power and reclaim the Mishima Zaibatsu. The revenge-fueled Kuma II assists his master in his journey.
- Lili Rochefort decides to retrieve Pandora for the sake of her father, but unable to do so alone, she is forced to ask her rival, Asuka Kazama, for help.
- Marshall Law has a mountain of debt, but after learning of Pandora from the news program and smelling the scent of money, he decides to travel to the South Pole with Paul Phoenix.
- The current head of the Mishima Zaibatsu, Jin Kazama, suspects the mysterious box is somehow connected to his cursed Devil Gene and decides to head towards Antarctica to find out. Ling Xiaoyu accompanies him out of fear that the box may be dangerous to him.
- Ogre hears a familiar voice from his past and heads to the location of Pandora in Antarctica, where the voice came from.
- Lars Alexandersson seeks to destroy Pandora to prevent an eminent war between the Mishima Zaibatsu and Shadaloo. He asks Alisa Bosconovitch to assist him on the mission, to ensure neither group obtains the box.
- Bryan Fury, who seeks to steal Pandora for himself, raided a G Corporation lab at the South Pole gaining total control of a Jack series robot known as Jack-X.
- Christie Monteiro and investigator Lei Wulong are searching for Christie's teacher Eddy Gordo when they discover a lead placing Eddy in the Antarctic with the Mishima Zaibatsu and Shadaloo's forces. The two work together to find Eddy and to keep Pandora out of the wrong hands.
- Mega Man heads to the South Pole after learning about the box from Roll, who believes the box to be a satellite from an ancient civilization.
- Pac-Man and his seemingly living, wooden mech suit (similar to Tekken's Mokujin) head for Pandora, their origins a mystery.
In addition to granting the personal wishes and hidden desires of others (as seen in the episodes and endings of the game), Pandora can cause a person's natural strength to skyrocket to levels beyond their own natural strength, and can also awaken, merge, and potentially influence, with other inner powers, as seen in Ryu and Ken's ending; it can also reject other sources of power, such as Bison's Psycho Power.
However, Pandora eventually corrupts the minds and souls of those under its influence, even artificial life forms; its ability to influence minds has considerable range, being able to reach out to Akuma's place and other beings throughout the globe from its landing site. Pandora's energy also has addictive qualities; those who are affected by its dark power become far more violent and dangerous, and lose self-awareness and control of themselves.
The energy is so powerful, it can even bring the dead back to life, and can heal a person, as well as cure sicknesses of any kind, as shown in Chun-Li and Cammy's ending.
The body of someone under the influence of Pandora takes on a black/purple hue with white and pink markings; their eyes glow red, their hair glows white, and their voice turns dark as well, mostly gaining an echo effect (in Heihachi Mishima's case, his entire body will just turn red).
During gameplay, Pandora can be triggered if the character the player is currently controlling has less than a quarter of their health remaining. When used, it provides a slight power boost to their partner, and an "infinite" Cross Gauge (i.e. EX Specials and Super Arts can be used as many times as desired). However, there are two notable drawbacks:
- Pandora requires the sacrifice of the current character. This is not necessarily a drawback; one can trade in a partner on their last slivers of health for a more powerful character. However, this does not guarantee the user the advantage.
- A meter appears above the user's life meter. Upon triggering Pandora, the user will have a limited time to win the match afterward; if the user fails to end the match before this meter runs out, the character is knocked out, thus causing them to forfeit the round.