Long before the arrival of the Imperium, the kingdom of Ultramar was ruled by Roboute Guilliman, the last king-warrior of Macragge. Even after learning his true origin as a Primarch, the son of the Emperor of Mankind, he seeks to expand his holdings both with word and force, through the single-handed subordination of the XIII Legion, the Ultramarines. Now, facing a hostile Imperium in the world of Toas, Guilliman must carefully choose his weapon—otherwise his dreams of a bright future will never come true.