The contrast between their powers. Naruto has his ninja techniques like Rasengan and Shadow Clone Jutsu, while Escanor has his incredible strength that varies with the time of day. When combined in a fanfiction, it creates unique battle scenarios. For example, in a fight against a powerful enemy, Naruto could use his clones to distract while Escanor delivers a powerful blow at high noon.
The different worlds they come from add to the allure. The ninja - filled Hidden Villages of Naruto's world and the medieval - like setting with magic in Escanor's world. A fanfiction can blend these two settings in creative ways. It could be a story where Naruto's village is threatened by a force from Escanor's world and they have to work together to save both their homes. This mix of different elements from two distinct universes makes the fanfiction very interesting.
Their personalities are also very different. Naruto is a determined and often goofy character, always looking to improve and protect his friends. Escanor, on the other hand, is proud and confident, with a sense of honor. In fanfiction, seeing how they interact, whether they clash or become friends, is really engaging. They can learn from each other's values and grow as characters, which makes for a great story.