Flit Asuno is the first protagonist of Mobile Suit Gundam AGE. Though he does not remain the primary protagonist, the series essentially serves as a chronicle of his life: he is seen as a child, teenager, young adult (in Universe Accel/Cosmic Drive), middle-aged man, senior citizen, and is implied to have died of old age at the end of the series. He loses his mother in an attack by the "Unknown Enemy" (UE), and is driven by hatred and the desire to be a savior ever since; these feelings are reinforced by the events that occur during his time aboard the battleship Diva.
Flit is born in the year 101 of the Advanced Generation calendar, the same year that the first UE attack ("The Day the Angel Fell") occurred. In AG 108, Flit's home space colony of Ovan is attacked by the UE; his mother is crushed by rubble, but not before handing the AGE Device to her son. Using the data inside the AGE Device, Flit builds Gundam AGE-1 and the weapon-building system known as the AGE Builder. In AG 115, Flit's new home, Nora, is attacked by the UE. He initially asks Federation pilot Largan Drace to pilot the Gundam, but circumstances would cause Flit to operate it himself. Flit defeats the UE machines, but not before Nora is damaged beyond repair. During evacuations, he happens upon Yurin L'Ciel. As the two exit into space, they are attacked by more UE machines; it is here where Flit begins to exhibit precognitive "X-Rounder" abilities.
After leading Yurin to safety, Flit begins to serve aboard the Diva battleship. After resolving a conflict at the space colony Fardain and spending time with Yurin at the Minsry colony, Flit and the the Diva crew return to space in order to attack the UE base at Ambat. During the operation, child soldier Desil Galette reveals that he has captured Yurin and forced her into the Farsia mobile suit. Using Yurin's X-Rounder abilities, Desil attacks Flit in a two-on-one battle. Yurin regains control of the Farsia just in time to receive a fatal blow that was intended for Flit. As the Farsia explodes, Yurin sends one final telepathic message to Flit before dying. Flit proceeds to rip Desil's Zedas into pieces in a blind rage. Now determined to eradicate the UE, Flit infiltrates Ambat. It is there that Flit and the rest of the Diva crew learns that the UE are actually "Vagan," humans that were part of a Mars colonization effort gone wrong. This doesn't change Flit's views, and he insists that they are not human.
Sometime after Flit's chapter, he marries childhood friend Emily Amond and has two children: Asemu and Yunoa.
In Asemu's chapter, Flit is the commander of the Earth Federation's space fortress Big Ring. He takes time off from his job to pass the AGE Device to Asemu. After Asemu has joined the military, Flit boards the Diva battleship once again so that he can lead on the front lines. He pilots the AGE-1 Flat several times, clashing with Desil in one instance. At the end of Asemu's chapter, Flit exposes the Federation leader's ties to the Vagan, and initiates a purge of Vagan-alligned government officials.
As Asemu disappears following the birth of his son Kio, Flit helps Asemu's wife Romary raise the young boy. However, Flit secretly trains Kio with a battle simulator so that he may continue the fight against the Vagan. After a surprise attack on the city of Olivernotes, the now-retired Flit requests a battleship; after repeatedly being denied, Flit is finally given the long-outdated Diva and a thrown-together crew headed by rookie captain Natora Einus. Flit initially leads the Diva crew to victory, but upon reaching space, Kio is kidnapped by the Vagan and taken to their home colony of Second Moon. Kio is rescued by his father (who was previously discovered as a pirate captain), but the young teen begins to question Flit's motivations.
In the final arc of Gundam AGE, Flit is reinstated into the Earth Federation forces and pilots the AGE-1 Gransa. During the battle to reclaim a Lunar Base from the Vagan, Flit successfully shoots down artificial X-Rounder Girard Spriggan after she goes berserk. In the final battle at La Gramis, he sees an opportunity to eradicate the Vagan once and for all with the Plasma Diver missile, but is stopped by Asemu and Kio. Kio's X-Rounder power invokes a vision of Yurin who begs Flit to forgive his enemies. Finally having a change of heart, Flit uses the Plasma Diver to get the attention of the Federation and Vagan forces. Together, they prevent Vagan's Second Moon from being destroyed by the out-of-control Vagan Gear.
In the years between the Battle of La Gramis and the official conclusion of the war in AG 200, Flit is honored as a hero. A statue is erected in his honor, and his Gundam AGE-1 is featured in a museum.