Well, a plot could revolve around Villain Deku trying to recruit Uraraka to his side. He might start by showing her the flaws in the hero society that she's a part of. Uraraka, initially resistant, starts to question her own beliefs as Deku keeps presenting her with evidence of the corruption and inequality. This could lead to a very complex relationship between them, where she's torn between her loyalty to the heroes and the allure of what Deku is offering. Or perhaps there's a parallel universe where Deku was always a villain and Uraraka is the only one who can reach the part of him that was once good.
A plot twist could be that they are being manipulated by a greater villain. They think they are in control of their actions as villains, but in reality, someone else is pulling the strings. This could lead to them realizing they are not true villains at heart and decide to turn against the real villain. Another possibility is that their villainous actions cause an unexpected reaction from the hero society. Instead of just fighting back, the heroes come up with a plan that forces Villain Deku and Villain Uraraka to re - evaluate their motives. For example, the heroes might start to offer amnesty to minor villains, which makes them wonder if they should continue on their villainous path.
Maybe Villain Deku and Toga team up to take down a common enemy that has wronged them both in the past. As they work together, a strange and dark relationship forms between them. Toga starts to develop deeper feelings for Deku, but he's only focused on revenge at first. However, over time, his view of her might change.
A possible plot is a power struggle between them. Since Deku has turned villain, he might see Bakugou as a threat to his plans. Bakugou, on the other hand, wants to bring Deku back to the light. This creates a constant back - and - forth of battles, both physical and psychological, as they try to outwit each other.
A possible plot is that Villain Deku has a plan to destroy a major hero institution, and Hero Deku has to stop him. But when they meet, Hero Deku realizes that Villain Deku was once like him, full of hope. This makes Hero Deku hesitant to fight at full force. Or perhaps Villain Deku has kidnapped someone close to Hero Deku, and during the rescue mission, Hero Deku tries to convince Villain Deku to change his ways. Also, they could be from alternate universes where the roles are reversed, and they are forced to interact and learn from each other.
Well, a plot could involve a power struggle. Villain Deku has some new and dangerous powers that he uses to challenge Kacchan. Kacchan, being the proud hero he is, refuses to back down. Along the way, they start to understand each other better. Maybe Deku's villainy is a result of some misunderstanding or being pushed too far by the hero society. As they interact more, they might find a way to reconcile their differences and even work together to change the hero society that led Deku astray in the first place.
For Villain Deku, his character can be developed by showing his descent into villainy. Maybe he starts off with small acts of rebellion against the hero system that he once idolized, gradually becoming more extreme. His relationship with Uraraka can be a catalyst for this change, either pushing him further into the dark side or causing him to question his actions. For Uraraka, she can develop by having to face a friend - turned - enemy. This forces her to grow stronger, not just in terms of her quirk, but also emotionally as she has to deal with the betrayal.
One interesting Deku and Uraraka fanfiction could be about them going on a special adventure together in a new part of their world. Maybe they discover a hidden power that only they can unlock when they work together.
For Villain Deku, with One For All, he could start to use it in combination with other dark or unethical techniques. Maybe he learns how to transfer the power in a more dangerous and unpredictable way, not for the good of others but to create a power - hungry following. As for Villain Uraraka, her zero - gravity power could be enhanced with some sort of negative energy. Instead of simply making objects float, she could make them float and then smash them into other things, causing harm. Her power would be warped from its original heroic intention of assisting and rescuing to causing harm and destruction.
One idea could be that Deku gets tired of being constantly underestimated and bullied despite his efforts to be a hero. So, he decides to use his knowledge of hero strategies against them and becomes a villain. He could form his own group of outcasts who were also treated unfairly in the hero - centered society.
One idea could be that Deku, turned villain, challenges Bakugou's view of heroism. He could expose the flaws in the hero society that Bakugou blindly believes in. For example, Deku might target the way heroes are ranked and how it creates a cut - throat environment. This would force Bakugou to re - evaluate his own pursuit of being the top hero.