Maybe they believed that Hermione had some sort of special power even as a baby that could be both a danger and an asset. By kidnapping her, they could control and train her in a way that would benefit the fight against the Dark side. For example, if she was showing signs of extremely powerful magic at a young age, they may have wanted to ensure she used it for good from the start.
It's also possible that there was some sort of internal conflict or misinformation within the Order. Perhaps someone in the Order received false information that Hermione was in some way connected to the Dark side (even as a baby, which sounds absurd but in the world of fanfiction, anything can happen). So they kidnapped her to investigate and keep her away from what they thought was a potential threat.
One possible motive could be power. In some fanfictions, there might be dark wizards or witches who believe that Hermione, being a very intelligent and magically gifted child even from a young age, could be used to their advantage. They might think that they can control her magic or use her knowledge for their evil plans, like finding ancient magical artifacts or unlocking powerful spells that are otherwise inaccessible.
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.
One possible motive could be to use Hermione as a bargaining chip against Harry Potter. Since Hermione is his close friend, the kidnappers might think they can force Harry to do something, like give up a powerful magical item or valuable information.
Another motive could be related to her family. Maybe there was some sort of blood feud or an old grudge against the Grangers. The kidnappers could have thought that by taking Hermione, they could get revenge on her family. In some fanfictions, there are secret magical families that have long - standing rivalries, and Hermione's kidnapping could be part of that.
One possible motive could be that Sasuke has been consumed by his thirst for power. In the Naruto universe, Sasuke has often been shown to be willing to sacrifice a lot for power. In this fanfiction set in the Wave arc, perhaps he sees Sakura as an obstacle to his pursuit of power, either because she tries to stop him from following a dark path or he believes she will hold him back in some way.
In these fanfictions, a common motive for Hermione's kidnapping could be her unique knowledge. She is known for her extensive reading and understanding of magic. Some villains might want to use that knowledge for their own gain. For example, they could be looking to uncover ancient and powerful magic that Hermione has studied. Regarding the adoption part, it might be a way for those who kidnap her to control her future. They could think that by 'adopting' her, they can shape her into someone who serves their interests better. It could also be related to a prophecy. If there is a prophecy that involves Hermione in some way, certain groups might kidnap her to either prevent the prophecy from coming true or to make it come true in a way that benefits them.
Well, Obito could be doing it out of revenge. He has a long - standing grudge against the Hidden Leaf Village. Naruto is seen as a symbol of hope in the village. So, by kidnapping him, Obito could be trying to strike a major blow to the village's morale and show that their so - called 'hope' can be easily taken away.
Another reason might be revenge. There could be a character who has a grudge against Inuyasha or someone close to him. So, they kidnap him to make him suffer or to use him as bait to draw out his friends. For example, if there was a demon whose family was slain by Inuyasha in the past, they might kidnap him for revenge.
One possible motive could be some sort of mind control. Maybe a powerful enemy has the ability to control Percy's actions and forces him to go after Artemis. This would add an element of tragedy as Percy would be acting against his will.
Well, it might be that the kidnapper has some sort of medical need that they think Kaoru can fulfill. Since she's a nurse, they could be desperate for medical attention that they can't get through legal means. Or perhaps there's a villain in the fanfiction who just wants to create chaos in the hospital by taking one of its nurses, and Kaoru happened to be the unlucky one.