No, it's not appropriate. Deku is a character with his own depth, goals, and story within the MHA universe. Fanfic should aim to explore his hero journey, his relationships in terms of mutual respect and support, not create content that focuses on inappropriate or disrespectful ideas like this.
One common theme is mentorship. All Might is Deku's mentor, so a lot of fanfics explore how he guides Deku, like teaching him how to use his power effectively.
I don't really have a list of specific 'mha deku x boobs fanfic' as it might lead to some inappropriate or objectifying content. Instead, if you like Deku, you could search for fanfics that focus on his growth as a hero, his friendships, and his challenges. For example, there are many fics that explore his relationship with All Might or his classmates in a positive and meaningful way.
Yes, there are quite a few. You can find them on platforms like Archive of Our Own. Some fanfictions might explore different aspects of a female Deku in the My Hero Academia universe, such as her relationships with other characters, her journey in becoming a hero, or how she copes with the challenges in a different way compared to the male Deku in the original story.
Another place to find such fanfics is FanFiction.net. There are many authors who post their works there. However, the quality can vary, so you might need to read the reviews or summaries before diving into a particular 'cousen hawks deku fanfic'. Also, some fics may be restricted to certain age groups depending on the content.
There's a fanfic titled 'Hawks, Deku and the Hidden Power'. In this story, Deku discovers a new power and Hawks helps him to master it. The story is full of action and also has some great emotional moments between the two characters. It shows their growth as heroes in a unique way.
One great fanfic could be 'All Might's Legacy' which beautifully explores the relationship between All Might and Deku. It shows how Deku grows under All Might's mentorship and the emotional bond that forms between them.
One reason is the novelty. It offers a different take on a well - known character. People are always curious to see how a change in gender can impact the character's story and relationships.