Well, usually in such a manga, the girl is held against her will, maybe in a secluded place. There could be attempts to rescue her by friends or heroes, and lots of tension and drama along the way.
It might be. True stories often get turned into books to raise awareness or share someone's harrowing experience. But one would need to research the background and author's claims to confirm its authenticity.
Perhaps the anime girl was kidnapped because she holds a special key or knowledge that the military guards want. She could be from a world where anime rules apply, and her knowledge of that world's magic or technology is what attracted the military's attention. She will then go through a series of adventures within the military compound, making friends with some of the inmates (if there are any) and planning her great escape.
Start with a bang. You could describe the moment of the kidnapping vividly. For instance, 'The anime girl was walking down the dimly lit alley, her long hair flowing in the gentle breeze. Suddenly, a hand clamped over her mouth and she was dragged into the shadows.' This immediately grabs the reader's attention.
One common plot twist could be that the kidnapper turns out to be someone the anime girl thought she could trust, like a seemingly friendly acquaintance. This adds an element of betrayal to the story.
One possible motive could be for experimentation. They might believe the anime girl has unique abilities that could be harnessed for military purposes, such as superhuman strength or special psychic powers.
In fanfiction, if an anime girl is kidnapped by the military, it could lead to a story of rescue. Maybe her friends or some heroic characters will start a mission to save her. They might have to face various challenges set by the military, like security systems and trained soldiers.
One possible plot is that the guy in the van is actually under the control of a more powerful villain. The anime girl, who might be a key figure in the anime's lore, is kidnapped to be used as a bargaining chip. However, during her captivity, she befriends a small creature or another captive in the van. Together, they come up with a plan to escape and expose the real villain behind the kidnapping.