The contrast between their characters. Saiki with his extraordinary powers and Satou who tries to be as ordinary as possible. This contrast creates a lot of comical and heart - warming situations in the fanfic.
Well, 'The Adventures of Saiki and Satou' is a great one too. It takes them on various adventures, both in the school setting and outside. The author does a wonderful job of exploring their personalities through these adventures and how they grow closer as a result.
Nendo could be a great addition. His simple - minded yet loyal nature can add some humor and unexpected twists. For example, he might accidentally almost expose Saiki's powers while trying to be helpful in a situation involving Teruhashi.
The Saiki K manga ended. It wrapped up the storylines and gave a satisfying conclusion to the readers. Although it's over, it still holds a special place in the hearts of fans.