As a whole Marbet's personality is a naturally calm and kind person. She is also very strong-willed, willing to do what it takes to do what she thinks is right no matter how hopeless it seems, and can work through the pain of injuries. While not horribly temperamental per se, Marbet can be very opinionated. Though she likes him, Marbet initially feels envious of Uso when he is repeatedly sent on sorties by the League Militaire, despite herself being the designated pilot. These feelings recede however as the series goes on and she learns to respect Uso's abilities. Similarly she initially feels disgust towards Shrike Team leader Oliver Inoe describing him as being "like a pimp", but later it is revealed that she was in fact jealous as she marries and is impregnated by him.
Marbet's story in Mobile Suit Victory Gundam begins with her piloting the titular LM312V04 Victory Gundam's Core Fighter. She is being chased by a Zolo and a Shokew from the Zanscare Empire's BESPA force, Yellow Jacket Team. Her Core Fighter is damaged by the Zolo's attack, but she manages to damage both of her pursuers and allow Uso Ewin to subdue the Shokew in a brawl with Chronicle Asher. Marbet returns to the League Millitaire base with an injured leg. Shortly after Uso returns in the Shokew being attacked by the Yellow Jackets. Realizing that it is him in the MS Marbet supports him by firing on his attackers with a beam rifle in the hands of the Victory Gundam's top.
Marbet soon sorties again in the core fighter in order to lead the Yellow Jackets off from their Camion truck. She launches in the Victory Gundam's Top Fighter and is successful in shooting down an enemy Zolo, shortly after however her Top Fighter is shot by Chronicle and crashes.The League Millitaire take in the Top Fighter for repairs, and after seeing Uso struggling in his captured MS, she launches in the Victory Gundam's Core Fighter and recovers him back to their camp. She later aids him again by sending him Core Blocks in battle. After seeing his success on the battlefield despite his age, Marbet considers that Uso may be a Newtype, she later asks him to fight in her stead, due to her injuries. A day later however she launches to support him, but crashes her Core Fighter. Endeared to the children in the League Millitaire, Marbet begins to take an active role in encouraging them and stopping disagreements.
Another battle against the Yellow Jackets occurs a short time later and Marbet yet again launches in the Core Fighter, she becomes locked in a combat with a Tomliat, she thinks that she can defeat it using the full Victory Gundam, but after docking and forming the Victory Gundam she decides she is still outmatched and swaps out of the Gundam for Uso.
Marbet assists Uso with repairs to the Core Fighter and is accosted by Oliver Inoe, who tries to talk to her, but gives up after she repeatedly ignores him. He says that he will talk to her later and departs. Their interaction seems to imply a preexisting relationship and Uso comments that the exchange is like a marital argument.
Marbet assists in preparations for the League Millitaire, along with the Shrike Team, to make an escape using a disguised transport plane. She, Oliver and Uso all launch together in Victory Gundams, the plane is damaged and while Uso battles, she and Oliver help keep it flying by holding it's wing's underside and using their engines to boost it. Throughout several later battles Oliver and Marbet continue to support Uso with their Victory Gundams.
When the League Millitaire launches a shuttle into space Marbet acts as the copilot. She then finds that Uso and most of the children have snuck aboard. They abruptly make her wears stockings over her head and take pictures of her pretending to be a terrorist taking over the shuttle. Once they reach space the shuttle approaches the orbital energy satellite Hiland. There they find BESPA forces. They are captured and taken aboard a Zanscare Patrol ship, however they make a successful escape.
Before they meet up with the Reinforce Junior and Guanland the group is forced into battle again and Marbet begins using a captured Zoloat. After the battle is over Uso expresses his disgust at the leader of the League Millitaire, Jinn Jenham. When Junko Jenko begins displaying a clear death wish after most of the Shrike Team has died, Oliver tries to support her, Marbet does so as well, and when Junko nearly dies by her aggressive actions, Marbet stops her from proceeding. At first Junko is angry, but soon thanks her and the two have a drink together.
Shakti has disappeared along with Suzy Relane, the baby Karlmann Dukartuse and dog Flanders, they flew out a hull breach into space. Uso feels that they are still alive and Marbet and Junko realize that he intends to search for them. They ambush him atop his Gundam's Core Fighter and affectionately force him to reveal his true reason for leaving. Despite this they do not realize that he does in fact end up at Side 2 in search of her and Marbet is surprised to find him there when the League Millitaire attack the Zanscare capital.
Shortly after the events at the Zanscare capital Uso and Marbet are captured and the are sentenced to face execution, but are saved by the rest of the team with the help of the Queen. Marbet again goes into battle, this time using a Gun-EZ.
After the events at Side 2 the Reinforce Junior lands on a Macedonian Colony and the crew ask to be seized as POWs by the colony authorities in order to hide from BESPA forces. during their time in the camp, the League Millitaire formulated a plan to escape which involved Oliver and Marbet being married. Despite this act apparently being a ruse, the two make it clear that they do in fact want the marriage and Oliver asks Marbet to bear him a child, she agrees.
The two engage in combat again, when not long after their escape from Macedonia, the Reinforce Junior is forced to contend with the Motorad Squadron. In this battle Oliver dies tragically in an ineffectual suicide attack against the Adrastea. After his death she quickly moves on with her life in an effort to escape the pain, but becomes more aggressive in her attacks upon her enemies. She is shocked and horrified when she realizes that she has attacked several enemies while using Odelo Henrik and Tomache Massarik as shields. After this battle she cries over Oliver's ashes, they spread into space. Odelo and Tomache change the head on the Victory Gundam Hexa that Marbet has been using to a standard Victory Gundam head in order to honor Oliver.
Marbet begins to show a further leadership role and as she did when they were often together in the Sinopes, she begins to lead when Odelo and Tomache become pilots and they gain the White Arc. She fights alongside the others as the continue to attempt to stop the Adrastea on the Earth, but to little avail. After a complicated chain of events she ends up stopping Uso from his attacks on the Adrastea after a sudden cease fire is declared. Shortly after this she is the first to be passed the remains of his mother by a crying Uso - her decapitated head in a helmet.
A little while after these battles, Marbet begins feeling ill. The reason for this is later revealed to be the fact that she is pregnant. Even once she realizes this she chooses to continue fighting and begins experiencing Newtype flashes. The revelation dawns on her that her child is a Newtype.
Marbet leads the others in the White Arc in order to investigate the Angel Halo. She continues fighting contending with opponents such as Katejina Loos and Fuala Griffon. In the end she survives and returns as she nears childbirth, to a grave made to honor her late husband Oliver, she stays in Kasarellia awaiting her child's birth along with Uso Ewin and Shakti Kareen.