One evening at FATE, Dominique finds Sion in the bar and gives him a necklace, a present for his one-year anniversary as a bouncer. Suddenly, Mikado Group's special forces burst into the bar and kidnap Dominique.
Dominique is taken to Mikado's headquarters and lies unconscious in the Crystal Dome. After many battles, the bouncers arrive to rescue her, but Dauragon C. Mikado stands in the way. Sion says they've come to take her back, but Dauragon tells them he's Dominique's brother, and she has returned to him. Dauragon then battles the bouncers. After they beat him, he knocks Sion to the ground and sends them down a trap door.
Dauragon then watches over Dominique's still form. Dauragon remembers their past. His flashbacks reveal that when they were children, they had no home and no parents. Dominique was very sick, and in the rain, Dauragon carried his little sister on his back. He tried to get medical help from a hospital, but the hospital turned them away, and Dauragon had to wander the streets with Dominique. Eventually, a car stopped them. The car's owner turned out to be Master Mikado; he saw Dominique's condition and immediately drove them to a hosptial. Dominique, however, remained sick. Master Wong (Dauragon's and Sion's martial arts master) told Dauragon that Master Mikado wanted to adopt Dauragon and make him his heir. Dauragon, out of gratitude for the help Mikado gave Dominique and himself, agreed to become worthy of the honor.
Meanwhile, the bouncers have been split up inside the Mikado Building. If you follow Sion's scenario, he comes across a computer with information on the bionoids and surgical enhancements Mikado has experimented with. Sion finds an entry, titled "Aggelos Anastasius," with Dominique's picture, but the entry is locked...
Eventually the bouncers find Dominique at the top floor of the Mikado Building. Insane Mugetsu is waiting for them, and they fight him. After the battle, Sion runs to Dominique's side and wakes her. Sion's so relieved that she's alright that he embraces her, and Dominique is startled and happy- this is the first time Sion has ever hugged her. The others remind them they have to escape.
They get in the elevator; while inside, they hear an announcement over the speakers that there are intruders in the Rocket Tower. Kou says that with the four of them, they'll easily stick out. Dominique softly apologizes (for hindering them), but Kou says he didn't mean that, they just need a decoy. The group decides to split up with two bouncers distracting the enemies while the other bouncer and Dominique escape.
If you choose Sion, Dominique is happy. If you choose Kou, Dominique is only a *little* reluctant to accompany him. In this section of the game, Dominique just runs after the bouncer who's supposed to guard her. However, she takes damage from the enemies, so if she dies, the game ends. Once the bouncer and Dominique successfully reach the elevator, they descend downwards.
On the lift, if the bouncer with Dominique is Volt or Kou, Dominique explains her fears to him. She asks him if it's alright for her to stay with Sion. She feels guilty that the bar was destroyed because of her. Dominique doesn't like it here so she ran away from it before, and that's how she met Sion and everyone else. Volt and Kou reassure her that she has helped Sion and Sion needs her.
If she's with Sion on the elevator, she asks him, "Can I stay with you always?" Sion, surprised, asks, "What's this, all of a sudden?" Dominique says she doesn't like it here, and it was Master Wong who helped her escape. Sion is surprised that his master assisted her. Dominique continues that after she began to live with him, he didn't talk much to her at first. However, for the first time she was free and happy. Sion is obviously touched by her words. Dominique asks if they can go home together; he hugs her and says of course. She closes her eyes and smiles happily.
Unfortunately, as Dominique and the bouncer try to escape from the Rocket Tower, a PD-4 appears and captures Dominique. It says Dauragon is waiting for Dominique. Dominique struggles and says she's going home with Sion. The robot knocks her out then challenges the bouncer. The other two bouncers arrive to help fight it. Once the PD-4 is defeated, Sion rushes to Dominique's side. Before he can reach her, though, even more PD-4s appear and surround the men.
Dominique wakes up, sees the PD-4s, and screams Sion's name. Her call reaches Mikado's satellite, and something weird happens to her. Her face separates slightly from the head, and you can see machinery inside. Her parts do their things, and Dominique, expressionless, suddenly gets to her feet and quickly beats all the PD-4s. Dominique then falls to the ground, and steam rises from her body. If you play with Kou, he says Dominique has been "activated."
Before the bouncers can reach her, Mugetsu captures Dominique and takes her to Dauragon in the shuttle, the Galeos. Sion falls to his knees, completely stunned at what he's just seen. "That was Dominique?" It's then that Volt tells Sion and Kou that Dominique is the dead sister of Dauragon. Dominique died from a terminal illness. Dauragon would, and did as the new head of Mikado, do anything to bring Dominique back to life. Dominique is thus a bionoid. Sion doesn't believe him, but Kou points out they have no choice but to rescue Dominique and discover the truth.
Meanwhile, on the Galeos, Dauragon uses Dominique to control the satellite, which is his main reason for having her kidnapped. First, theydestroy the hospital that refused them so long ago.
Once the bouncers reach the Galeos, they fight Kaldea. If you defeat her with Sion, Kaldea reveals that Dauragon and Mikado Group did experiments on her in an attempt to make Dominique more human.
The bouncers then confront Dauragon. Dauragon explains how he will use the satellite to rule the world, since humans just really want to be absolutely controlled. The satellite destroys more places on Earth. Sion cries out for Dominique to stop, and though she remains unconscious, she visibly struggles. Dauragon becomes angry and asks what's wrong, and Volt says that Dauragon's younger sister doesn't agree with him. Dauaragon only laughs bitterly and says, "Younger sister?" He says Dominique is just a puppet. Sion is furious since Dauragon is the one who made Dominique like this.
The bouncers fight Dauragon, and after Dauragon is defeated twice, they go to Dominique. Dominique wakes and says that she had a horrible dream where she killed a lot of people. Sion comforts her and tells her it was just a bad dream. He promises she won't have any more dreams like that, and he hugs her.
Depending on the scenario, Dominique may tell the bouncers how to escape Galeos before it crashes into the satellite. She says that in her dream, she saw the Galeos split into two pieces, and the aft section returned to Earth. Volt and Kou are sceptical, but Dominique insists it's true, and Sion believes her. The three go to the back of the Galeos before it separates, and as they return to Earth, they watch the other part collide into the satellite.
Sometime later at FATE, everything is pretty much back to normal. However, if you see Volt's ending, Volt tells Sion that eventually Dominique will learn her true nature (as a bionoid). She will see how they all become old while she stays forever youthful.
At the end of the game, Dominique stands in front of a grave. She wears Sion's necklace, so it's probably his grave. She then sees a dog that is like the one Sion has on the back of his shirt. Dominique lifts it up and laughs.
If you defeated Dauragon with Sion, you'll also see Sion and Dominique's first meeting.