Darin was well-known by the people of Laus for his uneasiness to Ostia, always claiming that Laus should be the strongest of the Lycia territories. However, under the influence of Ephidel, a servant of Nergal, and the Black Fang, Darin began preparing his territory for full-scale rebellion against Ostia. Unknown to him or the Laus soldiers, this was actually a well-conceived ploy by Nergal to cause a war between Lycia that would generate enough quintessence for Nergal to open the Dragon's Gate.
Unfortunately, his plans were deterred by Marquess Pherae, Lord Elbert, and Marquess Santaruz, Lord Helman. Elbert was brought to the Dragon's Gate to be sacrificed because of his strong quintessence, and Helman was quickly disposed of by Ephidel, but not before pointing Lords Eliwood and Hector to Laus.
With the two lords coming to investigate the disappearance of Marquess Pherae, Darin sends his son, the cavalier Erik to dispose of the two lords and their companions with aid from the Laus cavalry. Eliwood, Hector, and their companions prove too strong with the aid of the tactician (if he is present), Erk, and Priscilla, and the Laus cavalry are beaten back. With the forces dwindling, Darin, persuaded by Ephidel, leaves the remainder of Erik's forces to Eliwood's and Hector's forces and flees. But after the battle, Erik tells the lords everything he knows, and for a moment, Eliwood is in denial. It is unknown where he was when Sealen invaded the castle.
With nowhere else to go, Darin captures the territory Caelin as well as its marquess, but Lyn and her vassals, Kent, Sain, Wil, and Florina escape the siege of the castle. The three lords are reunited at the base of the castle and best General Bauker. With his plot nearly unraveled and cornered in Caelin's fortress, Darin secretly departs from Caelin with Ephidel, leaving the remainder of Laus's army to be decimated by the lords' forces. Bernard, the Knight Commander of Laus, is killed by the lords in his trust that Darin will come and help, leading up to the disbandment of most of Laus's armed forces, until when they join Bern in FE6.
However, Darin was not safe from the curiosity of Eliwood, searching desperately for his father. Aided by the Ostian spy, Leila, the company arrives at Valor, despite the Black Fang's best efforts to deter them. Uhai, one of the strongest Black Fang members, is noted to have died trying to delay the three lords. With his objective nearing completion, Darin holds the forward defenses of the Dragon's Gate, defending the throne ferociously with his Spear (Silver Lance and Hand Axe in Eliwood Mode). He underestimated the three lords, however, and was killed in the aftermath of the siege of the Dragon's Gate.
Darin reappears as a morph in the second battle of the Dragon's Gate, resurrected by Nergal with the legendary morph weapon Rex Hasta. He is defeated in the battle, and is seen smiling as he dies a second time, apparently finding peace. His son, Erik, would join him in death 2 1/2 decades later, fighting Roy's army under Nacien's orders, with help from the Sacae-Bernese myrmidon Rutger, who joins the Pheraen forces when Clarine speaks to him.