Naruto's reaction could be a mix of sadness and resolve. He has a big heart, so the betrayal would cut deep. But he also has the will of fire within him. He could use this as fuel to rise above the situation. He might seek out new allies in the High School DxD world, like Issei and his friends (if they weren't part of the betrayal). Together, they could work towards uncovering the truth behind the betrayal and taking on any threats that might be related to it.
He could be betrayed by a false friend in the DxD world who spreads lies about him. For instance, telling others that Naruto has a hidden agenda to take over their realm.
One possible fanfiction idea could be that Naruto, who somehow ends up in the world of High School DxD, is betrayed by some of the devils there. Maybe they initially seem friendly but then backstab him for his power or because they fear his potential. Naruto, being the resilient character he is, would then have to find a way to overcome this betrayal and prove himself.
Naruto might initially feel disbelief. He's used to seeing the good in people, so Akeno's betrayal would be a huge shock. He could go into a state of self - doubt, wondering if he misjudged her all along.
Naruto might be angry at first. He is not one to take betrayal lightly.
One way could be through the power system. The EMS (Eternal Mangekyou Sharingan) from Naruto could be a unique power that a character in the High School DxD world acquires. Maybe a transfer student from a hidden ninja village arrives at the high school and has to keep their EMS a secret while dealing with the devils and angels in the school. This could lead to some interesting battles and interactions as the powers of the EMS, like the ability to use powerful jutsus, contrast with the magic and abilities of the High School DxD characters.
Power struggle is also a frequent theme. Naruto is a powerful ninja, and in the High School DxD world, power is highly coveted. His powers might attract the wrong kind of attention, and those who want to gain or maintain power could betray him to eliminate a potential rival.
Naruto characters' reactions would vary. Shikamaru would likely find the whole situation troublesome. He doesn't like getting involved in things that are too complicated. But Naruto would approach the archangel with his usual enthusiasm. He'd want to be friends and learn about the archangel's world. Hinata would be shy but also intrigued. She might see the archangel as a very noble and powerful being. And Kiba with Akamaru would be a bit more aggressive in their approach, ready to defend themselves if needed but also eager to know more about this new entity.
He would be heartbroken. Naruto has a big heart and has always trusted his friends. This betrayal would be a huge shock to him.
Naruto would be deeply hurt. He has grown up with so little love and acceptance in the village, and Hiruzen was one of the few people he thought cared for him. His reaction could involve a lot of self - reflection. He might question his own worth and what he has done wrong. But ultimately, his positive nature would take over. He would try to understand Hiruzen's reasons, even if he didn't agree with them. And he would strive to find a way to reconcile and make Hiruzen see that he is not a threat.
At first, Naruto might try to reason with the Western side. He would want to understand why they betrayed him. He believes in the good in people, so he would hope that there was some misunderstanding. However, if they continued to be hostile, Naruto would become determined. He would gather his own allies, like his friends from Konoha, and form a resistance against the Western forces. He would use his powerful jutsus and his unwavering spirit to take on those who wronged him.