Definitely Naruto. His popularity stems from his growth throughout the Naruto series and his ability to make friends and allies easily. In this fanfiction, when paired with the Justice League, he stands out. Another popular one is Batman. His detective skills and strategic mind are fascinating, especially when dealing with the more mysterious aspects of the Naruto world. Kara is also loved for her kind heart and powerful abilities which make her a great bridge between the two universes.
Popular characters include Naruto for his energetic and determined nature. He's always ready to jump into action and his ninjutsu skills are really cool. Kara is popular because she has a relatable backstory in the DC universe and her superpowers are amazing. Wonder Woman can also be a popular character in this fanfiction. Her warrior spirit and unique powers can create interesting interactions with the ninjas from Naruto's world, like when she exchanges combat techniques with female ninjas.
Naruto is often a very popular character as he brings his unique ninja skills and his never - give - up attitude. Kara (Supergirl) is also popular as she represents the powerful and heroic side of the Justice League. Superman can be popular too as his superpowers are always exciting to see combined with the ninja techniques.