One of the popular characters paired with Sarutobi is Jiraiya. They are both important figures in the Hidden Leaf and their relationship, whether it's as comrades or as teacher - student in some fanfic interpretations, is always interesting to explore.
Orochimaru is also often paired with Sarutobi in fanfics. Their complex relationship, from Orochimaru being Sarutobi's student to turning into a villain, offers a lot of room for creative storytelling. Writers can explore different 'what - if' scenarios in fanfics.
Obviously Naruto would be one of the main characters interacting with him. Naruto would look up to Sarutobi as a mentor and a source of knowledge. Their interactions could range from training sessions to deep conversations about the future of the village.
Well, it might not be as mainstream as some other types of Naruto fanfics. While the idea of Naruto being a Sarutobi fan has potential for interesting storylines, it may not appeal to the broader fan base as much as, say, fics focused on the main battles or relationships like Naruto and Sasuke's. But among certain groups of fans who like exploring unique character dynamics, it could be quite popular.
In some fanfictions, the previous Hokages could be main characters in relation to Mirai Sarutobi. For example, the First Hokage Hashirama Senju's spirit could appear to give Mirai some wisdom or a special power. Or the Third Hokage, being from the Sarutobi clan as well, could have left some hidden knowledge that Mirai discovers, making the old Hokage an important part of the story.
Obviously, Naruto would be one of the main characters. And since it's about him being the son of Sarutobi, Sarutobi himself would be a crucial character. There would also likely be the usual Naruto characters like Sasuke, Sakura, Kakashi etc. as they would still be part of Naruto's life in the fanfiction, even with this new family relationship.
I'm not entirely sure as the term 'senal' is rather unclear. It could potentially be a very specific fan - created story within the Naruto universe involving Sarutobi. Maybe it's a fanfic that reimagines Sarutobi in a new and unique way.
Hiruzen Sarutobi is definitely one of the most important. As the Third Hokage, he has a wealth of knowledge and power. His actions and decisions have a huge impact on the clan and the village. Another important character could be Asuma Sarutobi. He is a skilled ninja and his relationships with other characters, like Shikamaru, add depth to the fanfiction.
One consequence could be that the village runs more smoothly. With the paperwork out of the way, decisions can be implemented faster.
Sasuke is often paired with Naruto in these fanfics. Their dynamic, whether as rivals or friends, can be further explored when Naruto is in his fox form. Sasuke might be intrigued by Naruto's new abilities or help him control the more wild aspects of the form.
Another reason is that it allows fans to explore different aspects of the Naruto world that were not fully shown in the original series. For example, Sarutobi's relationships with other clans and his influence on the development of new ninja techniques. Writers can take these elements and create unique and engaging stories.
One popular 'badass sarutobi fanfic' might be the one where Sarutobi shows extraordinary combat skills against a powerful enemy. It could involve him using unique jutsu combinations that are not typically seen in the original series.