Big Sister

Big Sister by Academia Nut (The author of Thousand Shinji and The Open Door) is a story with a similar premise to Lovehammer: A Magical Girl ends up in the Warhammer 40000 universe before the Heresy and leaves a big mark. But the similarities end there.

When the future Primarch Vulkan arrives on Nocturne, he does not arrive alone, a teenaged girl, still recovering from crippling injuries even before somehow finding herself stranded on a Death World, comes across the infant Primarch and brings him to the nearest settlement through sheer force of will.

The two grow up together as the girl recovers, eventually helping her little brother battle Dark Eldar Raiders. The girl takes the nickname of Ga’ri, meaning "Ash Maiden", a name she finds fitting, despite the sometime negative connotations that come with it. As she regains the use of her magic, Ga’ri also helps her "Little Brother" grow in mind and spirit as fast as he does in body. When The Emperor lands on Nocturne, he finds his lost son to be a very different man than even he was expecting.

"“Please tell me that our mission will be to assassinate those idiots and I get to use the sniper rifle this time.”."
 * Amazon Brigade: The Gae'ri, a team of female psykers modeling themselves after Vulkan's sister.
 * Anyone Can Die:
 * Big Sister Mentor: Ga'ri. It's right there in the title.
 * Chaste Hero: Vulkan explains to how he doesn't get love.
 * Cool Big Sis: Half the point of the story is Ga'ri being this. To a Space Marine Primarch, mind you.
 * Curb Stomp Battle:  and does not last very long.
 * In a more humorous example, Ga'Ri in Vulkan and the Emperor's game. To quote the Emperor,
 * Determinator: Ga'ri for using all of her power to shelter the infant Vulkan . Also for singlehandedly recovering from the wounds and infection sustained for doing so, and finally standing up on her own two feet after the first Dark Eldar attack and literally defining the concept for Vulkan.
 * Heroic BSOD
 * Get a Hold of Yourself, Man!: Vulkan uses his head and delivers one to the Night Haunter.
 * My Name Is Not Durwood: One of the reasons Ga'ri takes up the name is that it turns out that the problems certain people had in saying her name in her own series are even worse when the local tongue doesn't even have some sounds common in Japanese.
 * Oh Crap:
 * Puelammi
 * See also the Reveals below
 * Papa Wolf: When, Vulkan is not happy.
 * That Came Out Wrong: "I want your sister." -Beat- " “Correction, the Order needs your sister on its side."
 * The Reveal: It's hinted but never outright stated until the third chapter, when, that Ga’ri is.
 * Secret Test of Character: Vulkan's first training with the Salamanders.
 * Shout Out: Vulkan asks Jaghatai Khan "What is best in life?". Three guesses what Khan says his original answer would have been.
 * After killing a Dark Eldar raider: "If it bleeds, we can kill it."
 * "Heeeeere’s Konrad!"
 * "Even if the Mon-keigh were here and had launched at the same time as us, to get through the interference in the Warp would take some sort of navigational genius..."
 * Vulkan built a proto-force weapon on Nocturne with a hand-pumped charcoal forge.
 * Silly Reason for War: A planet rebels against the Imperium because The Emperor's eyes are the "wrong" color. As one Scout puts it:
 * Vulkan built a proto-force weapon on Nocturne with a hand-pumped charcoal forge.
 * Silly Reason for War: A planet rebels against the Imperium because The Emperor's eyes are the "wrong" color. As one Scout puts it:


 * Too Fast to Stop: When Ga'ri puts up a barrier in the way of a Dark Eldar speeding at her, the results are... crunchy.
 * The Woobie: You'll want to hug Konrad Curze.