History:The RX-0 Unicorn Gundam is first operated by the Visit.
Foundation as part of the "UC Project" at the Industrial 7 colony.
In the manga version the RX-0 Unicorn Gundam was first used on a test run. Four ARX-014 Silver Bullet units three with GM heads and one with a Gundam head attack Gundam Unicorn. Cardeas Vist was trying to see Gundam Unicorn's full potential by testing it against Londo Bell's Silver Bullets. The Gundam was outnumbered four to one, then three of the Silver Bullets used their remote beam gun forearms to grab hold of the Gundam and started electrocuting the pilot. Before one of units could take down the Unicorn, the pilot activated the Unicorn Gundam's Destroy Mode and took down one of the units. He then went after the other, destroyed it, and only one Silver Bullet remained. 

The Unicorn launched at full speed towards the remaining Silver Bullet, but at the last moment the Gundam returns to its Unicorn mode as the pilot dies due to the stran of the NT-D.
In the anime the Unicorn is first seen as it flew by the colony at an extremely fast rate, but Banagher was able to make it out as a mobile suit. The Unicorn Gundam is piloted by a Vist Foundation Pilot, Gael and the head of the House of Vist. Cardeas Vist put a lot of stress on the pilot when they entered a debris field during a test excercise near the Colony Industrial 7. When the test ended Gael notified Cardeas that some people might have seen the MS, but Cardeas said that the people would probably think it was a shooting star.
When an intense battle between the Londo Bell taskforce led by the Nahel Argama along with the ECOAS special forces, and the Neo Zeon remnants known as "The Sleeves" broke out, Industrial 7 became the battleground between the two sides. The battle was halfway over and Banagher was looking for Audrey Burne (the girl he rescued earlier) when he found the Mobile Suit that he saw on the test run. He found Cardeas Vist in the Cockpit of the MS. Banagher and Cardeas talked and before he died, Cardeas entrusted the mobile suit to Banagher and soon realized that Cardeas was his father. Banagher took the Unicorn Gundam and headed out, only to be confronted by Marida who was in the NZ-666 Kshatriya. In the initial skirmish, the Unicorn took her all the way outside the Colony.
As soon as the Unicorn Gundam and Kshatriya got outside the colony and into space where the Nahel Argama is, they separate out so they can face each other in combat. 

Immediately, Marida deploys the funnels toward the Unicorn. Inside the cockpit as Banagher spot the funels from the Kshatriya approaching at him; suddenly, the NT-D system self-activated. A field is deployed briefly to deflects the beams fire from Kshatriya's funnels allowing Unicorn Gundam to proceed with its transformation. Marida is frightened while watching the Gundam resembled figure transforming. Right after activating its Destroy mode, Unicorn Gundam draws out its Beam Saber as the crews of the Nahel Argama watching and astonished by the Destroy-mode Unicorn Gundam. The Unicorn Gundam engages the Kshatriya, destroying most of its funnels and chopping off two of its binders before it retreats. The Unicorn then transformed back into its normal state with a unconscious Banagher still in the cockpit. 

The Second Coming of CharShortly afterwards, Banagher deployed the Unicorn a second time, against Full Frontal's MSN-006 Sinanju - itself a testbed frame used in the development of the Unicorn - armed this time with the shield and Beam Magnum. Banagher expends the Beam Magnum's ammunition, in futile attempts to shoot down the Sinanju, but none of his shots connect though one of them, narrowly missing one of the AMS-129 Geara Zulu escort units, nevertheless causes it to explode. The NT-D activates a second time and Unicorn gains the advantage. However, Marida launches in the Kshatriya against him again. During the ensuing match the NT-D's time limit runs out and the Unicorn deactivates. With Banagher unconscious, the Unicorn is captured by the Sleeves and taken to the Neo-Zeon asteroid colony Palau.