Write an interesting, riveting, lengthy alternate history short story in the form of a crossover fanfic chapter of a fanfic of Fate Stay Night/Prisma Illya, Magika Kenshi, Call of Duty, Halo, and Eromanga-sensei with plenty of action, dialogue and exposition, in which the UNSC [United Nations Space Command] and its immediate predecessor, the UNSA [United Nations Space Alliance] was created as part of a secret agreement between the United States, the German National Socialist Workers' Party and the Greater Germanic Reich when the later became the CDU and the Federal Republic of Germany after their loss in WW2 in order to combat the threat of a hypothetical monster invasion of the human world as well as the threat of rouge magicians and the moonlit world. The UNSA/UNSC operates as a secret organization that will stop at nothing to protect humanity from the threat of the supernatural, using the advanced technology developed by the National Socialists in their wonder weapon programs to deal with rouge magicians and monsters while also remaining in the shadows. Sagiri Izumi is an alias that Illyasivel von Einbern uses while out in public and Hana Umezono aka the famous light novel writer Muramasa Senju, is in fact an identity that Sakura Matou uses to move around in the non-magical world to avoid attention from rouge magic users and the Clocktower. Elf Yamada aka Emily Granger is actually Reines El-Melloi Archisorte, and her rivalry with Illya aka "Sagiri" and Illya's twin, Chloe von Einzbern, who is known as Megumi Jinno in public, is due to Illya's relative ignorance of the ways of the higher ranking families of the Clocktower. Sagiri locks herself in her room when she comes home from school because she is afraid her beloved adoptive big brother Masamune Izumi will find out that she has become a magical girl. 

Of course, Masamune is clueless to the truth about his family or the fact that Hana and Emily are even magicians, being concerned with getting through the day.

Meanwhile, a combined squad of UNSC/UNSA Marines and SPARTANS, the elite genetically engineered warriors of the UNSC's military force, decide to pay Fuyuki City a visit after UNSC command in Texas receives reports of suspicious activities from its spies in the area. The UNSC squad quickly tears through the magical underworld of the sleepy Japanese town, even managing to take out Shinji Matou and his grandfather Zouken without Sakura Matou being aware of their involvement. Not even the monsters which turn into Class Cards when defeated aren't safe from the UNSC/UNSA squad, causing Illya's mistress Rin Tohsaka and Rin's bitter rival, Luvia Edelfelt to be confused when they investigate the aftermath. Neither Illya/Sagiri, Sakura/Muramasa/Hana, Rin nor Luvia have any clue about who is behind these brazen attacks or even about the existence of the UNSC/UNSA.

The chapter ends with Masamune opening Sagiri's room door to check up on his adoptive little sister only to see Sagiri about to have a discussion with Reines as Emily/Elf, Sakura as Hana and Chloe about the mysterious happenings in Fuyuki. He is surprised that Sagiri even has a social life and attempts to close the door to give her privacy, but Reines as Emily uses the opportunity to try and one up Sagiri, telling him that the girls were discussing how to confess their love for him. Sakura as Hana then secretly uses her magical powers to push Sagiri/Illya on a shocked Masamune, causing their lips to touch. Masamune realizes that Sagiri has been using a sarashi to bind her breasts as he feels the weight of her huge boobs on his chest, causing him to blush as he tries to hide his erection. 
