Kaldea was a girl about Sion's age whom he met 9 years ago while he was training under Master Wong. She asked him what he was doing, and he told her he was training. She said it looked fun, but when Sion told her no one was stopping her from doing it, she said she got sick easily. Sion asked her her name, and she introduced herself as Kaldea.
From then on, the two were very close friends. Kaldea was always there for Sion through his triumphs and pains. After Kaldea congratulated Sion for getting Master Wong to use one of his hands in a fight, she said that he and Master Wong got along well. Sion thought that Kaldea had very caring parents, and she remarked that if never scolding her meant they were caring, that was true. As the two children grew up, they eventually fell in love.
Two years earlier, Kaldea got a job at Mikado. Sion gave her a pendant as a gift even though she thought it was expensive. She told him she would treasure it. However, very soon after, Sion heard from Kaldea's parents that there was an explosion at Mikado, and Kaldea was killed. Sion became extremely depressed and violent after Kaldea's death. He fought anyone and wanted someone to kill him. That was eventually how he got his job at "Fate" - by challenging Volt, the current bouncer, and after being defeated, the Boss offered him a job.
In the present, a mysterious woman with black hair appears in Mikado. She is usually always at the side of Daugaron C. Mikado. This woman has the ability to shape shift into a black panther. The panther skulks around, watching the bouncers, particularly Sion.
The black panther first appears near Central Square. The bouncers are attacked by special forces from Mikado, and after the fight, they see the black panther. The panther and Sion stare at each other, and when Volt asks Sion if he's ever seen it before, Sion says he hasn't.
Later, a black haired woman plays the piano inside the Crystal Dome at Mikado. Sion, from a tree outside, hears the music and recognizes the song. The woman stops playing, transforms into the black panther, and goes to Dauragon's side. After Dauragon kills Wong, the bouncers enter the dome. Dauragon and the black panther fight them. At the battle's end, Dauragon attacks Sion, and the bouncers fall into a trap pit. Dauragon then watches Dominique and remembers their past. The black panther is by his side, and when his flashbacks end, it transforms into the woman.
If you choose Sion for the Mikado Building, then you see more of the black panther and the woman. Otherwise, you don't see her again for a while. Sion makes his way through the building. After he passes through a door leading to a restricted area, he sees the panther. The panther, though, does not attack him but only stares at him before materializing through another door. Sion follows it and finds a computer with information on all the experiments the Mikado Group Corporation has done on bionoids.
Sion is stunned to read how Kaldea, the girl he loved, was an experiment at Mikado. He remembers the two of them together and thinks that the explosion wasn't an accident. The following is the entry Sion reads about Kaldea:
"Biological Engineering II: Bionoid Experiment
Upon evaluating the unanticipated side effects manifested by the PD series, we intend to broaden our research related to cloning. Our best example of this project is Kaldea. The one drawback with our present technology is the treatment ages the subject's cells approximately 10 biological years."
After Sion leaves the room, he enters a long hallway with a closed door at the end. As he struggles to open it, the black panther materializes through a wall behind him. They fight. After Sion wins, the panther turns into the black haired woman. She looks at him sadly and says, "You don't recognize me, do you?" Sion is confused, but the woman turns back into the panther and disappears.
The panther does not appear again until the bouncers reach the Galeos. This time, she fights as both the panther and the woman. If you fight with Volt or Kou, Kaldea collapses after the battle, saying, "Si...on..." Volt/Kou asks Sion if he knows the woman. Sion says that the woman looks like someone he once knew in his past, but that person died.
If you fight with Sion, Kaldea reverts to human form after the battle. She says Sion's name. He comes up short. She says that he doesn't recognize her because she's now so much older than he is. Stunned, Sion puts two and two together and realizes that she is Kaldea. He runs forward to catch her in his arms. She explains that her death was faked by Mikado so that they could do bionoid experimenton on her; their main goal was to make Dominique become more human. Kaldea says the reason she stays with Dauragon is because she pities him; inside, he is lonely. Kaldea says Sion he has to stop Dauragon.
If you don't get Kaldea's ending, Dauragon interrupts the lovers' reunion. Furious at her words, he throws his chain through her body, killing her. He tells her he doesn't need sympathy from a bionoid and leaves. Sion is obviously livid at his love's murder.
To get Kaldea's ending, you have to choose to play as Kou or Volt after you defeat Dauragon for the first time (when the bouncers are separated in Mikado), then choose Sion when you fight Kaldea for the last time in the Galeos. Kaldea won't die after being defeated. She gives the same story as above, then tells Sion that she's alright and closes her eyes. He lies her on the ground and goes to confront Dauragon.
After you defeat Dauragon, Kaldea will appear and tell the bouncers that the shuttle has an automatic separation sequence- once the shuttle nears the satellite, the shuttle will separate into two parts: the front section will connect to the satellite, and the back portion which will return to Earth.
As they run towards the aft section, the sequence starts. Kou and Volt reach the other section of the shuttle as a metal door slowly closes that section off. However, Kaldea obviously more hurt than she let on; she clutches her chest as she runs. Sion notices and slows down for concern. Volt uses his strength to try to prevent the door from closing, but he can't hold out much longer.
Kaldea suddenly looks determined and thinks, "Sion...!" With her last ounce of strength, she shoves Sion and Dominique underneath the closing door. She collapses on the ground, still on the other side that will collide with the satellite. Sion turns to her and calls her name. Kaldea tells him she can't go with him, and she's not the one who needs him now. Tears fill her eyes, and Sion yells, "Kaldea!" As the door closes, Kaldea says, "Take care, Sion..."
The bouncers and Dominique watch the front of the shuttle crash into the satellite and explod. Sion thinks that Kaldea can rest in peace now.