The Earth has been plagued by Demons, Villains, Aliens, Monsters, even Kaiju for the better part of the century. In the past, government agencies, NGO's, vigilantes, and even normal people have fought for mankind's existence alone, with varying levels of success. But it's a new century— no, millennium, and the United States has a new President: Billionaire Industrialist and all-around Magnificent BastardDavid Xanatos. As the most powerful man in the world, Xanatos wants to make sure the world is still there, and key to that is making sure all these extra-normal defense groups start playing nice together, so he's starting at Stargate Command.Which leads us to SG-1 having to ride herd over a meeting between the President, UNIT director Hyppolyta Trevor, JSDF Lieutenant Tetsuya Tsurugi, and a sweet little girl named Nanoha Takamachi...It can be found here.
Death Is Cheap: Deconstructed. It is explained that most superheroes only lasted half a decade of activity at best before either being crippled, dying, going insane or at best retiring. Some were to the point that UNIT or the FBI shut them down when they were tracked down.
Fiction as Cover-Up: UNIT had long ago adopted a policy of "information leak" that funded the production of comics, movies, books and TV shows that fictionalized re-named and exaggerated the exploits of superheroes to provide their superpowered agents cover.
Kick the Dog: Millenium loves this trope, but Wodan Ymir takes the cake for hunting down mages drained by the Wolkenwritter and killing them whilst they were weak, when they did their best not to kill anyone.
These incidents, however, went largely unnoticed by the public at large due not just to the intervention of the US Government and the actions of some occult organizations with an interest in keeping humanity in the dark, but as well as humanity’s own capacity for self deception and general stupidity. So great was this combination, that few people outside of the directly affected areas even know about the beings involved, and even then, there are some who still do not believe.
Technically, you could just count the entire series, since Majin has alreadyMade allusions to Subaru already existing, albeit as a small child who has yet to A: Meet Nanoha, and B: grow up to her Striker(s) age.