Well, in such a fanfiction, it often explores a different side of Deku being a villain and his relationship with Todoroki. It could be about how their dynamic changes from the original story. Maybe Deku as a villain has different motives and goals that somehow involve Todoroki, like trying to use Todoroki's power for his own evil plans or trying to turn Todoroki to his side.
One common theme is the exploration of their complementary personalities. Todoroki is often seen as reserved and Momo as intelligent and responsible. Fanfics like to show how these traits can create a harmonious relationship.
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.
The theme of self - discovery is also prevalent. Both characters grow and learn more about themselves through their interactions. They discover new aspects of their powers, emotions, and identities as they navigate their relationship in these fanfics.
Another theme is cooperation. Given their different quirks, fanfics often explore how they can work together effectively. Like in a battle scenario, Momo can create useful items and Todoroki can provide offensive and defensive power with his ice and fire abilities.
One common theme is redemption. Since Endeavor has made many mistakes in the past regarding his family, especially with Todoroki, many fanfics focus on him trying to redeem himself. Another theme is forgiveness. Todoroki has to decide whether to forgive his father or not. And also, family bonds. They are father and son, so exploring how they can strengthen or repair their family connection is often seen in these fanfics.
One popular theme is friendship development. Writers often explore how Iida and Todoroki's different personalities interact and how they grow closer as friends.
One common theme is the power of friendship. Since they are both students in the hero academy, they often start as friends and then feelings might develop. Another theme is the overcoming of differences. Izuku was born without a quirk initially and Todoroki has a complex family background and powerful quirk. They learn to understand and support each other.
I don't encourage seeking out 'lemon' fanfiction which often contains sexual content. But if you want to explore the relationship between Villain Deku and Todoroki in a more appropriate way, you can join fan forums and ask other fans if they know of any well - written stories that focus on their dynamic, be it a more adversarial or a complex relationship that doesn't involve adult themes.
Power imbalance is often a theme. Deku might gain new, more dangerous powers as a villain, and Todoroki has to figure out how to deal with that. There could also be a theme of trust. Since Deku is a villain, Todoroki has to decide whether to trust him or not. And if he does trust him, it could lead to all sorts of complications in the story.