One possible plot could be that Harry is part of an experiment in a fictional world. The experimenters are trying to combine different species' abilities, and somehow Harry ends up being the subject that gives birth to kittens. It could then be about his journey of dealing with this new situation, taking care of the kittens, and facing the reactions of the people around him in that fictional world. This might involve him learning about the kittens' special powers or needs, and also dealing with the social implications of such an unorthodox event.
Well, it depends on the fandoms you're exploring. Some fanfiction communities are more likely to have such unique and creative concepts. You could also try joining relevant fan groups on social media platforms and ask if anyone knows of any 'harry gave birth to kittens fanfiction'. It's possible that it's a very niche or even a humorous take within a particular fan circle.
One plot idea could be that Harry is cursed by a dark wizard. The curse is designed to humiliate him by making him go through an unusual form of 'pregnancy'. As he nears the time to give birth, he discovers that the kittens have some special powers that could be used either for good or bad, depending on how they are raised.
If we consider this fanfiction idea, it might also involve other characters' reactions. For example, his friends would be extremely shocked at first. They might try to find a way to reverse the situation. And Harry himself would have to go through a physical and emotional journey. He would need to adapt to the idea of giving birth, which is something completely alien to him, all while being in a world full of magic and mystery.
Harry could be developed as a more nurturing character. Since he has to take care of the kittens, he shows a side of himself that is gentle and patient, which is different from his usual heroic self.
One idea could be that Harry discovers he has a magical ability that allows him to give birth to kittens as a form of new magic. The kittens could have special powers and Harry has to protect them from those who want to use the kittens for evil.
Well, it's a very strange concept. Maybe in this fanfiction, some sort of magic gone wrong causes Harry to have the ability to give birth, and the cupboard could be a significant place because it was his initial living space in the Dursleys' house. It might be a really wild exploration of magic and gender roles within the Harry Potter universe.
Another way is to have the kitten be a gift from a mysterious character. Maybe Dumbledore gives a kitten to Harry as a way to help him deal with the stress of fighting Voldemort. The kitten could have some sort of calming magic that helps Harry stay focused and centered during difficult times. This would add an interesting dynamic to their relationship and also give the story a new angle to explore.
Hermione would probably be very shocked at first but then would immediately start looking for a magical solution. She might rummage through her books to find spells to reverse the situation or make it safe for Harry.
Another theme might be the power and danger of potions. It could show how a seemingly ordinary potion - making class can lead to such an extraordinary and life - changing event for Harry. This would highlight the importance of proper potion - making and the consequences of mistakes or experimentation. Also, it could touch on the theme of acceptance. How do the other characters in the fanfiction accept or react to this very unusual situation? Do they support Harry or shun him? This could explore the different levels of acceptance within the magical community.