To create a believable character in a Highschool of the Dead fanfic, start with giving them a distinct personality. For example, if your character is a shy student, show how they react in the high - stress situations of the zombie apocalypse. Maybe they are hesitant to speak up even when they have a good idea for survival.
Naruto's experience in dealing with tough opponents in his own world would help him in the zombie - filled Highschool of the Dead. He would be able to quickly analyze the situation, figure out the weaknesses of the zombies, and come up with effective plans. His friendship - first approach might also lead to some interesting relationships with the other characters in this new and dangerous world.
The status of the Highschool of the Dead manga is rather unclear. There were some issues related to the author or publisher, and it just stopped without a definite conclusion.
However, it could also be someone like Madara Uchiha if he were to be part of this crossover. His vast power, knowledge of jutsu, and his ability to control the Nine - Tailed Fox would make him a formidable force. He could easily decimate hordes of zombies and manipulate the situation to his advantage, even in the unfamiliar highschool setting.
Well, first of all, the writers often take the unique elements from each universe. From Naruto, it's the ninjutsu, kekkei genkai, and the concept of the ninja villages. From Highschool of the Dead, it's the zombie apocalypse and the school environment. They then find ways to make these elements work together. Maybe a character with a Sharingan from Naruto can use its powers to detect zombies from afar. Also, they might use the character relationships. A Naruto character could form a team with some Highschool of the Dead survivors to face the challenges together. And they might also play with the different values of the two universes. For example, the loyalty in Naruto and the survival instinct in Highschool of the Dead.
I think Lucy would be really interesting. She could use her Celestial Spirit Magic in creative ways to deal with the situation in the highschool during the apocalypse. Maybe she could call upon spirits to help barricade areas or to scout for danger.