One interesting crossover could be the fight styles. In 'Kengan Ashura', there are intense martial arts battles. When combined with 'Naruto', ninjutsu could be pitted against those martial arts. For example, Naruto's shadow clone jutsu against a Kengan fighter's unique combat techniques. It would be a battle of speed, strategy, and power.
Goku from Dragon Ball Z would be an interesting addition. His Saiyan powers and love for fighting would make for some epic battles against the Kengan Ashura fighters. His ability to transform and increase his power levels would pose a great challenge to them.
One idea could be a crossover with another fighting anime like Baki. The fighters from Kengan Ashura could face off against the strong characters in Baki. It would be exciting to see their different fighting styles clash.
It could be Naruto. His vast array of ninjutsu, including the Rasengan and the ability to use the Nine - Tails' power, gives him an edge. He has experience in large - scale battles and has faced incredibly powerful foes. His ability to quickly adapt and come up with new strategies would make him a tough opponent against Kengan Ashura characters.
I'm not sure specifically which 'Karla Realistic Fiction' has distinct popular authors. But in general realistic fiction, authors like John Steinbeck are well - known. His works often depict the real lives and struggles of people. Maybe there are emerging authors in this Karla - related realistic fiction too.