One idea for a Naruto vs Todoroki fanfic could be that they are brought into a strange new dimension by some sort of magical entity. Naruto starts off with his usual energetic self, trying to figure out what's going on. Todoroki, on the other hand, is more cautious. Naruto might start with a simple Rasengan attack, but Todoroki uses his ice side to block it. As the battle progresses, Naruto realizes he needs to up his game and taps into his Nine - Tails chakra. Todoroki then decides to combine his ice and fire powers in an attempt to counter Naruto's new - found strength.
The most exciting scenario would be when Naruto goes full Nine - Tails mode and Todoroki uses his maximum ice and fire combination. Naruto in Nine - Tails mode is extremely powerful, with his chakra radiating and his physical abilities enhanced. Todoroki, when he combines his ice and fire, can create a powerful and unpredictable force. The clash between Naruto's brute strength and Todoroki's elemental control would be visually stunning and full of intense action. The environment around them would be completely transformed, with the ice melting and the ground shaking from Naruto's power.
Zuko's complexity makes him so interesting in these fanfictions. He has a troubled past which has shaped him, but he is constantly evolving. His ability to show vulnerability in front of the reader is another great trait. It allows for a deeper emotional connection between him and the reader, as seen in stories where he opens up about his insecurities and fears.
His friends would probably take care of him. Midoriya would be very eager to help, using his kind-hearted nature. He would make sure Todoroki is fed and comfortable.
One idea could be that all his friends at UA plan a surprise birthday party for him. They decorate the common room with his favorite colors, blue and red. Another plot could be Todoroki spending his birthday with his family, trying to reconcile with his father on this special day. Maybe he receives a heartfelt gift from his mother that has a deep emotional significance.
Todoroki's character development in time travel fanfictions can be quite profound. He may start as a somewhat aloof character, but through time travel, he begins to understand the importance of relationships more deeply. When he travels back and witnesses the relationships he could have had or lost, it makes him cherish the ones he has in his original timeline. His view of heroism also evolves. He realizes that being a hero isn't just about using his powers but also about making the right choices at the right time, which is especially highlighted when he has to make decisions that could change entire timelines.