He could wear a kimono to show cultural exchange. Hogwarts is a place full of different cultures, and a kimono is a significant part of Japanese culture. Wearing it might be a way for Harry to embrace and celebrate that culture within the wizarding world.
Hermione would probably be fascinated by the new magical knowledge that comes with the Japanese - influenced setting. She might be seen studying ancient Japanese spells and trying to find connections between them and the ones she already knows. And she might be wearing a kimono in a more proper and traditional way compared to the others.
He could wear a mask to protect his loved ones. If there's a new threat in the wizarding world that targets him and those close to him, a mask would be a way to keep his identity hidden so that his enemies can't use his friends and family against him.
He might wear a simple black - and - orange kimono, combining his signature colors. The orange could be used for the obi (the sash) and some accents on the black kimono, making it stand out.
One possible plot could be that Harry Potter is transported to a magical realm in Japan where he has to adapt to wearing a kimono while still facing his usual challenges like fighting dark wizards. Maybe he discovers new spells that are unique to this Japanese - inspired magical world and has to use his knowledge of both Hogwarts magic and the new magic he learns there to save the day.
Perhaps it's a symbol of unity. The fanfiction author might be exploring the idea of breaking down the house rivalries, and Harry wearing the Slytherin tie is a physical manifestation of that. He could be trying to show that Hogwarts should be united regardless of house.
In this fanfiction, Harry might be transported to a parallel magical world in Japan while wearing the kimono. There, he has to adapt to the different magical customs and traditions. He could meet Japanese wizards and witches who help him on a quest to find a way back to his own world. Along the way, he learns about the significance of the kimono in their culture and how it can be used as a magical tool.
However, it's important to note that when writing or reading such fanfic, it should be done with respect to the original source material and the cultures involved. The kimono is an important part of Japanese culture, and using it in this context should be a positive and respectful representation, not a means of cultural appropriation or disrespect in the Harry Potter fanfic world.
It could be part of a spell or a magical prank. Some fanfictions like to play with the idea of magic being used in creative and humorous ways. A spell might have gone wrong and made Harry want to wear a dress, or it could be a prank by Fred and George where they cast a spell on him to do so.
She might wear his clothes because of necessity. For example, if her own clothes got damaged or lost during an adventure. Harry's clothes would be readily available and a practical solution.
It could be for comical purposes. The idea of the powerful and heroic Harry Potter having to deal with something as mundane and embarrassing as wearing diapers can be quite humorous. It adds a touch of absurdity to the usually serious Harry Potter universe.