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.
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.
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.
One possible plot reason could be envy. Maybe Todoroki, as a villain in this fanfiction, is envious of Deku's popularity and the support he gets from fans. So, he kidnaps Deku to take away that source of admiration from him. Another reason might be related to power. If Todoroki has turned villain, he could see Deku as a threat to his plans, and by kidnapping him, he aims to neutralize that threat.
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.
Midoriya's friends like Uraraka and Iida would be extremely worried. They would immediately start looking for him. Uraraka might use her quirk to search in the air, while Iida would lead the ground search with his speed. Bakugo, on the other hand, would be furious. He would probably go on a solo mission to find Deku and take on Todoroki without hesitation.
Some popular themes could be the struggle of their relationship in a world that might not fully accept an omega - alpha pairing. For example, they might face challenges from society or their families. Another theme could be the power dynamics within their relationship. Since Todoroki is from a powerful family and Deku has his own unique power, how they balance that in their relationship is interesting. Also, themes of loyalty and trust often come up, as they have to trust each other in a world full of villains and danger.
To write this fanfiction without the 'lemon' aspect, think about their backstories. Deku's fall into villainy could be due to some great betrayal or a different view on hero society. Todoroki might be on a mission to either save or stop Deku. You can build a story around their ideological differences and how they interact with each other. For example, they could have a series of battles or encounters where they gradually understand each other more.
Writers often start with the established personalities from the original source. For Deku, they'll build on his determination and growth. They might show how his omega status affects his decision - making in relation to Todoroki. For Todoroki, his complex family background and his cool - headed nature are expanded. Writers may show how his alpha side influences his interactions with Deku. They also give them new traits based on the omega - alpha relationship, like Todoroki being more protective or Deku being more submissive in some aspects.