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.
A possible Naruto vs Todoroki fanfic could start with Naruto being on a mission in a world that is similar to Todoroki's. They cross paths and initially misjudge each other. Naruto thinks Todoroki is some kind of enemy ninja, and Todoroki is confused by Naruto's strange appearance and abilities. When they start fighting, Naruto's Uzumaki bloodline gives him an edge in terms of stamina. But Todoroki's unique quirk allows him to control the battlefield with his ice and fire. As the fight intensifies, they both start to respect each other's power and eventually, they might even team up against a greater threat that appears in this strange world.