Disclaimer: I do not own Code Geass, Clamp and Sunrise do.
In the Land of Warriors
In the Kingdom of Zilkhstan's capital, the City of Gralbahd, the people there lived under a heavily defended, if strict, atmosphere on account of Zilkhstan's highly competent military also being the main driver to the local economy through mercenary contracting. Despite the country's focus on profits in warfare, however, the Zilkhstanians were mostly content with their way of life as religiously guided by the Farlaf Order for centuries by the year 2017 Ascension Throne Britannia, during which time, power of the entire country was shared between the Holy Priestess of the Farlaf Order, Queen Shamna, and her younger brother who commanded the military, King Shalio.
Almost eight years prior to the date at the time, Zilkhstan's on and off enemy nation, the globally expanding Holy Britannian Empire, surprised the known world by offering the Kingdom custody of the children of the recently assassinated Empress Marianne vi Britannia as an official attempt to improve relations between the two monarchies. Even more surprising, their developing alliance had lasted even longer than what most people expected to the point that Zilkhstan not only aided Britannia in annexing multiple nations such as Japan, but that Queen Shamna was rumored to be engaged to the late Empress Marianne's only son, Prince Lelouch, to further solidify their partnership.
Unknown to the common masses, however, was that this growing union was formulated less due to political conveniences and more to machinations involving the supernatural power of Geass.
"I trust that your mother is doing well?" Shamna herself asked her fiancé while she and Lelouch were relaxing in the former's audience chamber within the Temple built inside the cliff surrounding Gralbahd, Shamna sitting on the fine-themed sofa as usual and Lelouch resting his head on the former's lap.
Despite what the official story said, Marianne vi Britannia only died in body eight years before while her spirit survived due to her individual Geass granting her the power to transfer her soul into another body, allowing her to survive the assassination. Although both Lelouch and Nunnally were intimidated to learn that the supernatural existed and that a grave enemy meant to do their family harm, they were still happy to know that their mother was still with them in one form or another.
As for the developing ties between Britannia and Zilkhstan, it was Emperor Charles zi Britannia's hidden intention, with the advice of the loyalist Geass Order's leader, C.C., that a reconciliation occur between the main organization and its centuries old splinter group, the Farlaf, to combat their common foe in V.V., a similar figure to C.C. and Emperor Charles' own brother, who planned on continuing the Ragnarok Connection to control all of Humanity. All the same, it was a positive bonus that Lelouch and Shamna grew genuinely close since they first met.
It was not an instant relationship on first sight, considering their youth at the time when their paths came together, but due to their similarities of having a younger sibling to look after alongside their developing intellects and inclination to pragmatic actions, they slowly emerged from strangers to close friends then lovers as they grew older.
"She is, my Queen." Lelouch answered Shamna's question with a flirtatious address and appreciative smile. "With Anya as her host, my mother is gradually becoming the Knight of Six again, so Nunnally and I might not hear from either of them for at least a while."
Caressing her fiancé's face, Shamna commented with. "Well, I'm sure they will both manage just as you and Nunnally will always be welcome to come here still."
With a nod, Lelouch replied. "Indeed, but enough about the sad details, Shamna, I'm more interested in you at the moment."
Humming in content, Shamna planted a kiss on Lelouch's lips that the young prince gladly reciprocated. As soon as they broke contact, Shamna responded. "I feel the same way, my handsome Emperor Lelouch to be."
If my fellow Code Geass fan, known online as PKD, is reading this, thank you very much for giving me an idea for how to make this pairing work in a one-shot. FanFictionNet's A Golden Meridian's adaptational good depiction of Nightmare of Nunnally's Eden Vital organization as written by Z98 helped, too. I had been meaning to work on Lelouch/Shamna for a long while, but the potential plot, even for a one-shot, kept escaping me.
I also have made some thoughts about Lelouch founding an organization modeled after G.I. Joe's Cobra, or Teenage Mutant Ninja Turtles' Foot Clan, and then opposing enemies unique to each respective franchise like Cobra-La and the Triceratons as crazy as it sounds, but I think I will be more likely to do Code Geass modeled after Spider-Man in one story, which may or may not be doing at a long pace like Lelouch of the Emerald Knights, and inserted in Voltron: Legendary Defender in another, which I would prefer to make different from Code Geass: Paladins of Voltron. We will just have to see in time.