For a 'Naruto x Highschool of the Dead' fanfiction, Naruto is a must - have main character. His presence is what makes the crossover unique. Among the 'Highschool of the Dead' characters, Saya Takagi would be an important main character. She's intelligent and resourceful. Naruto and Saya could make a great team. Naruto with his brute force and Saya with her brains. Then there's also Kohta Hirano, the gun - loving otaku from 'Highschool of the Dead'. He could be in awe of Naruto's powers and they could collaborate in battles against the zombies. Naruto could learn about modern firearms from Kohta, while Kohta could learn some ninja tricks from Naruto.
Obviously Naruto would be one of the main characters. He's the protagonist of the Naruto series, so he'd likely be at the center of the action in this fanfiction too. He'd be using his ninja abilities to combat the threats in the high - school - turned - zombie - land.
Obviously, Naruto would be one of the main characters. His determination and never - give - up attitude would be very useful in a zombie - filled high school. Sakura could also be a main character, using her medical ninjutsu to try and find a cure for the zombie virus. And Sasuke, with his powerful combat skills, would be great for fighting off the zombies.
Most likely Naruto himself would be one of the main characters. He's the titular character of Naruto. And probably some of his close friends like Sasuke and Sakura. From High School of the Dead, it could be Takashi Komuro.
Naruto could develop by learning to adapt his ninja skills to a more modern and zombie - filled setting. He might become more cautious as he realizes the different threats here compared to his ninja world. Rika could develop from being a normal schoolgirl to a more confident and brave fighter. She could learn from Naruto's fearless attitude and start using her own wits in more daring ways.
Most likely Naruto himself would be one of the main characters. Since it's a Naruto - based fanfic, he would bring his ninja skills and determination to the high - school - zombie scenario.
If we consider the Sharingan ability from Naruto, a character like Sasuke could use it to predict the movements of the zombies more accurately. This could be combined with the strategic thinking of the Highschool of the Dead characters. They could plan out how to best use Sasuke's ability to avoid large groups of zombies or to lead them into traps. The Highschool of the Dead characters might also learn some basic ninja stealth techniques from the Naruto characters, allowing them to move more quietly through the school corridors filled with zombies.
Maybe an evil sorcerer who has mastered both dark magic and some forbidden ninja techniques. He plans to use the chaos that would ensue from merging the two worlds to his advantage. He would be against Naruto and Gabriel because they stand in the way of his evil plans. He could start by creating unrest in the Highschool DxD world, pitting different factions against each other, and then try to use Naruto's presence as a scapegoat. Gabriel, being an angel of justice, would naturally oppose him, and Naruto, with his sense of loyalty and protecting others, would join her in the fight.
Some Naruto characters would likely be very confident in a Highschool of the Dead - Rei fanfiction setting. For example, Naruto himself would probably jump right into action against the zombies. He'd see it as another challenge to overcome and would use his Rasengan or other jutsus without hesitation. Sasuke, on the other hand, would be more calculating. He'd analyze the situation of the zombie apocalypse and the role of Rei and others before making a move.
Well, in this fanfiction, Naruto might arrive in the middle of the zombie apocalypse in the 'Highschool of the Dead' setting. His chakra and ability to sense danger could be a great asset. He could also form alliances with different groups in the high school. For example, he could work with the school's kendo club members, combining their sword skills with his ninjutsu to fight off the zombies. And perhaps he'd try to find a way to get back to his own world while also trying to save as many people as possible in this new and dangerous world.
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.