- Main article: War of the Lions
In S.947, Gunnar was plunged into a war with the other sons of Valius Reise Arnor V over his succession.
Initially considered the greatest threat to Prince Orthros, Gunnar's army was decimated with the power of the Vermillion Knight. With the remnants of his private army, Gunnar decided to join forces with the remains of his half brother Prince Albert's army to oppose the other princes. Their force was so large it should compensate for their lack of a Divine Knight.
Over time, he and Albert gained control over Magic Knights. With their power, Gunnar managed to hold off his half-brothers for a number of years. When the Vermillion Apocalypse, however, emerged in Heimdallr alongside the Infernal Castle in S.952, the armies of both Albert and Gunnar were completely annihilated.