Another motive could be related to security threats. If the anime girl is from a different group or species in the fictional world, the military might perceive her as a potential threat to national or regional security in the context of the story. So, they take her into custody to prevent any potential danger she might pose.
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.
The anime girl might be used as a bargaining chip. If there are different factions in the military or if there is some sort of political turmoil, the group that kidnapped her could use her to gain an advantage. For example, they could threaten to harm her if their demands are not met.
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.
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.
The motives could be revenge. Somebody who has been wronged by Deidara or the Akatsuki in general might kidnap him to get even. For example, a village that was destroyed by his explosives could seek vengeance.
One possible motive could be to gain power. Since Goten is a Saiyan, his power could be harnessed in some way. For example, they might want to extract his ki or use his DNA for some evil experiment.
One possible motive could be ransom. The kidnappers may think the girl's family is wealthy and they can get a large sum of money in exchange for her safe return.
Love or obsession could be a motive. Just like in some stories where a girl is so in love with a boy that she kidnaps him thinking it's a way to keep him close.
Revenge is another motive. Maybe someone has a grudge against the Reagan family for past actions. Nicky is an easy target to get back at them. For example, if the family put someone in jail, that person's accomplice might kidnap Nicky to make them suffer.
One possible motive could be ransom. Maybe some criminals knew that Christian was wealthy and thought they could get a large sum of money for his and Ana's release. Another motive could be revenge. Perhaps someone who had a grudge against Christian or Ana from their past decided to take this extreme measure.
One possible motive could be Bellatrix's loyalty to Voldemort. She might think that by kidnapping Hermione, she can get information about Harry Potter and the Order of the Phoenix. Hermione is known to be very intelligent and Bellatrix could believe she has valuable knowledge. For example, Hermione might know the location of Potter or the Order's plans against Voldemort.