At the onset of war, the empire's main strength was its fleet of Warrior MAs. Although these mechs could easily handle regular Dominion of Rubrum legionaries, the only hope they had of defeating the Agito Cadets of Akademeia was to outnumber them. The imperial MAs could not win against the dominion's Eidolons, and so MA pilots fled until the summoning had expired. Hoping to remedy the situation, imperial scientists devised the heavily armored Colossus and the airborne Helldiver MA models, which in turn helped spur the development of other models which would aid the anti-dominion offensive.
One of these is the Dáinsleif, deployed in the invasion of Akademeia. Dáinsleif is equipped with a crystal jammer, a device that nullifies the power of enemy Crystals, allowing the empire to paralyze all troops in Orience reliant upon their Crystal for strength. Dáinsleif's crystal jammer is just a prototype, however, and only a l'Cie could operate the jammer-mounted Dáinsleif.
Dáinsleif intercepts Machina Kunagiri and Rem Tokimiya, two Agito Cadets, at the arena, and renders the duo powerless with the crystal jammer. The two are saved by the cadets of Class Zero, who summon Odin against Dáinsleif much to Qun'mi's surprise. The cadets defeat Dáinsleif and it explodes, destroying the crystal jammer along with it while Qun'mi teleports to safety.
Dáinsleif is fought as a boss at the end of Chapter 1 at the Akademeia arena.
Dáinsleif is king Högni's sword, according to Snorri Sturluson's account of the battle known as the Hjaðningavíg.