In this fanfiction, Naruto would develop a new sense of responsibility. Since Pantera is a powerful entity in the DxD world, Naruto would have to be careful with its power. He'd be responsible for not misusing it and also for protecting it from those who might want to use it for evil. This new responsibility could change his carefree attitude a bit, making him more mature as he realizes the consequences of his actions in this new universe.
Naruto's confidence would probably grow even more. He already has a strong sense of self - belief from his experiences in his own world. But with Pantera in DxD, he'd be facing new and powerful foes. Every victory with Pantera's power would boost his confidence. He might also become more strategic as he combines his ninja strategies with the abilities of Pantera. He'd need to think about how to use Pantera's powers in the most effective way in battles against DxD's unique creatures.
Naruto may become more self - reliant. Since he's been neglected, he has to depend on himself more. In the DxD world, he learns new skills quickly as he doesn't have the support he once hoped for. This makes him a stronger and more independent character.
Naruto's development could be centered around his ability to adapt to a new culture. The Highschool DxD world has its own set of rules, ethics, and social norms. He would need to learn and respect these while still maintaining his own identity. His sense of justice might also be challenged as he realizes that the good - bad divide in Highschool DxD isn't as clear - cut as in his own world. This could lead to him re - evaluating his beliefs and growing as a character.
In this fanfiction, Naruto might initially struggle to control Pantera's power. Since he's used to his own chakra-based abilities in his own world. But as he gets to know more about Pantera in the DxD setting, he could start to master it. He might team up with some of the characters from DxD, like Issei, and they could go on adventures together, using Naruto's new - found power of Pantera to defeat common enemies.
His character would develop in his relationships. Naruto is very friendly and outgoing. In Highschool DxD, he'd meet all kinds of characters. He could start off being a bit naive about the romantic and power - related relationships in the school. But as time goes on, he'd learn how to handle them better. For example, he might have to deal with the complex relationship between Issei and the various female characters. This would make him more mature in handling relationships and also more empathetic towards different situations.
When Naruto wields the dark soul in the fanfic, his character development takes a sharp turn. He starts to view the world through a darker lens. His once unwavering loyalty to his friends and village may waver. He might become more secretive and less likely to trust others. His sense of humor could also disappear as the dark soul's influence seeps in. For example, he may no longer find joy in simple things like eating ramen with his friends. Instead, he'd be more focused on his newfound power and how to use it to his advantage, even if it means going against his former principles.
He might become more confident. With the added power from the serum, he would face challenges more bravely.
In many fanfictions, Issei's character develops in terms of power. He starts as a relatively weak character and gradually becomes stronger through training and various challenges. For example, he might learn new techniques from a mysterious mentor or gain new powers from a magical artifact.
Sasuke's character might become more open - minded. In the Highschool DxD world, he would be exposed to different cultures and ways of thinking. For instance, the concept of Devils and Angels having their own social structures would be new to him.
In some fanfictions, a well - known character might be given the energy sword. For example, Naruto himself could be the wielder. He could obtain it during a special training session or as a result of a new power - up. This would change his fighting style and give him an edge against stronger opponents like Sasuke or the Akatsuki members. It would also add a new element to his character development as he learns to master this new weapon.
In some fanfictions, Issei's character develops by becoming more mature. He realizes the consequences of his actions more deeply. For example, when he uses his powers, he starts to consider the collateral damage and tries to minimize it, which is a big step from his more impulsive self in the original story.