Naruto would likely be very energetic and take the lead in a battle. He'd use his speed and jutsu like Shadow Clone Jutsu to confuse the enemy. Mash, on the other hand, would be more cautious and use her shield to protect Naruto when he gets too reckless.
One plot idea could be that Naruto is summoned into the Fate Grand Order universe. He teams up with Mash to fight against the various Servants who have gone berserk. Naruto's unique jutsu like Rasengan could be a new and powerful attack in that world.
One reason could be the lack of promotion. Many fanfiction writers don't have the means or knowledge to effectively promote their work. So, even if they create an interesting 'Naruto x Fate Stay Night' crossover, it may remain unnoticed.
One possible neglected fanfiction could be 'Naruto in the Fate World' which might not have gotten as much attention but has an interesting premise of Naruto being transported to the Fate Stay Night universe and having to navigate its complex magic system and the Holy Grail War. It could have some unique character interactions and battles that blend the elements of both series.
A good Naruto Fate crossover fanfiction often has a well - thought - out plot that combines the unique elements of both universes. For example, integrating the chakra system from Naruto with the magic and Servant system of Fate in a logical way. It also needs to keep the characters in - character. Naruto should still be the determined and somewhat naive ninja we know, while the Fate characters should retain their own personalities.
One great Fate OC x Artoria fanfiction is 'The Unlikely Bond'. It delves into how an original character interacts with Artoria in a unique way. The OC has its own set of powers and beliefs that contrast and complement Artoria's. Another interesting one is 'A Meeting of Souls' which focuses on the emotional connection between the two. It shows how their different backgrounds lead to a deep and complex relationship.
One common theme is the clash of their personalities. Gilgamesh is proud and haughty, while Mordred is rebellious. Their interactions often involve power struggles and attempts to outwit each other.
One idea could be to have Taylor from 'Worm' end up in the 'Fate' universe and have to deal with the Grail War. Maybe she forms a pact with a Servant who is similar to one of her powers in 'Worm'.
Well, 'The Three's Paths' is also a good one. It delves into their past traumas and how they find solace in each other. Sasuke's brooding nature, Naruto's optimistic self and Gaara's new - found sense of belonging all come together to create an interesting dynamic in this fanfiction.
In these fanfictions, a common theme is redemption. If Sasuke has made some wrong choices, the story might focus on how Kakashi and Naruto help him find his way back. Also, teamwork is a big theme. How the three of them work together in different missions or challenges, and how their individual strengths and weaknesses play into that. It can also be about family - like relationships, as Kakashi can be seen as a father figure to some extent, and Sasuke and Naruto as brothers.