Rising From the Ashes Mk2 (42nd Millennium Lost Primarch Quest)

Gyril was a planet of gene-crafters who specialized in creating super soldiers from their slave populations and hiring them out as mercenaries. You arose from your pod outside the walled cities that were dotted infrequently around the planet, braving the deadly swamps and bogs for 5 years until you were captured as a slave during your sleep for the gladiator arenas. The lord of the walled city you were taken to, Lord Francis Crudelis, noticed your potential and saved you, instead training you in both the art of gene-crafting and close combat. You inherited the city after his death and worked to expand its area through the use of your revolutionizing proto-Astartes, the Sons of Strife. When the Emperor came for you, your walled city had grown to be the largest on the planet, and the Emperor himself recognized your skill in decoding the Astartes code from your own tissue samples.

Udamu was home to a feudal society of warlords battling with mid M1 technology (post Industrial Revolution but pre WW1) over the rich deposits of naturally occurring plasteel dotted along its surface. You were one of the first primarchs discovered because of this, the Emperor seeking to recover the precious material as early as possible into the crusade, almost at the same time as Horus and Leman Russ. Before the Emperor came, you were adopted by a champion of one of the warlords named Subaki, raised as his disciple in the art of the Burning Fist and its signature weapon the tonfa. Subaki challenged the Emperor in your stead given your apparent youth in his eyes, despite being almost the same height as him; he was loaned a suit of power armor and they went to battle. They were sealed inside a plasteel mine with enough air for 24 hours--at the end of the duration, the Emperor walked out holding an unconcious Subaki in his hands. The warrior had fought to the point of near death, and only when he began to suffocate did the warlord admit defeat. The next week, you departed with the Emperor, taking Subaki along as your advisor.

Punicia-IV was a tidally locked covered almost 90% by oceans. On the side of the planet facing the sun, humanity lived on a string of islands near the equator known Claustrum Chain, while the dark side of the moon held a race of aquatic xenos known only as the Deep Ones to the humans. Whenever humanity tried to expand their early M2 level civilization past the borders of the heliolatric zone, they emerged from the Oceans and terrorized humanity with genetically tampered abominations, reminiscent of early human settlers no less. Each time, the humans lost more and more territory to the xenos, unwilling to draw any closer than normal except during waves of outward expansions: it was during one of these waves that you arrived on the planet; for some reason, the slaves of the Deep Ones gave you a wide berth, keeping all humans away from you by proxy as well. It was only when the wave ended and the humans eventually retreated that you were found. At first, you were thought to be another trick by the Deep Ones, a spy meant to keep an eye on their infrequent prey. Your size and the various new and redundant organs in your body didn't help matters either - and so you were forced to walk the path of the outcast, living on the thin band between the heliolatric and tenebrilatric sides of the planet in vast state-ships with other outcasts. You grew into a survivor, and when humans rose up on yet another wave 12 years later, you were ready: you took your band of comrades in exile and joined the humans as guerilla fighters. Utilizing the fact that the slaves of the Deep Ones avoided you, you helped the humans of Punicia-IV to push the wave all the way to their city, arisen from the deep to defend against the intrusion. It was here that you first fought the Deep Ones in direct combat - 11 feet tall and almost as strong and as fast as a primarch with none of the strange fear of you their slaves possessed, they served as an extremely difficult challenge. Indeed, if it were any other primarch they may have fallen in battle, but you had 12 years of experience in driving off their lesser slaves, as well as the past half year of guerilla combat. You battled the king of the Deep Ones all across the city of the xenos, and after 6 hours of fighting you were beginning to get pushed back. After another 2 hours, the king had you on the ropes. Before he could strike the final blow, a flash of light blinded you, and the last thing you saw before falling unconcious was Horus battling the weakened Deep One King.