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.
A 'villain deku x villain todoroki fanfiction' might focus on their backstories that led them to become villains. It could be that they were both wronged by the hero system in some way. Deku might have been rejected too many times or faced unfair treatment, and Todoroki could have some family - related issues that pushed him to the dark side. The story could then show how they form an alliance and start their villainous journey together.
Perhaps they get involved in a power struggle within the villain world. They want to prove themselves as the most feared villains. This could lead to battles with other villains and alliances with some unexpected characters. It could also involve them trying to steal some powerful artifacts or secrets from the hero side to gain an edge in their villainous activities.
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.
One interesting crossover could be the magic system of Harry Potter being introduced to the MHA world. For example, a character from MHA might discover they have magical abilities like a Hogwarts student. Another could be the heroes from MHA having to face off against dark wizards from the Harry Potter universe. It would be a really cool mix of the two different power dynamics.
A lot of MHA Kaminari x Jirou fanfictions focus on the idea of mutual understanding. They come from different backgrounds and have different quirks, but through getting to know each other better, they grow closer. There are also themes of jealousy, like when one of them might get a bit jealous if the other is spending too much time with someone else. Also, their shared experiences at UA, like going through tough battles together, are often used as a theme to bring them closer in the stories.
Well, a good listener in a social story is like a silent supporter. They listen with empathy. That means they try to understand the feelings behind the words. For instance, if a character in the story is sad while talking, a good listener will pick up on that and respond in a kind way, maybe by offering comfort or just by being there for them.
To be a good listener, you need to show genuine interest, nod and make appropriate responses to show you're engaged. Also, don't be too quick to offer your own opinions until they've finished speaking.
Kaguya could be an interesting choice. She is extremely powerful and has a complex backstory. Her motives were initially self - serving and evil. If she were somehow resurrected or a situation where Naruto had to interact with her in a different time - line, it could make for a great fanfiction. Naruto's ideology of peace and friendship could clash and then potentially influence her.