The Doom Slayer and Vali would make for an exciting interaction. Vali is a very powerful and ambitious character in High School DxD. He would likely see the Doom Slayer as a rival or a potential ally in his quest for power. The two of them could engage in some epic battles or team up against a common enemy. Additionally, the interaction between the Doom Slayer and Koneko would be interesting. Koneko is a quiet and strong - willed character, and she might be curious about the Slayer's motives and his unwavering dedication to his mission.
Gohan and Issei would be really interesting. Issei is all about being a pervert and getting stronger in his own way. Gohan is this powerful yet humble Saiyan. Their different outlooks on power and relationships would create a lot of humorous and thought - provoking moments.
The Doom Slayer and a Space Marine would be really interesting. They both are combat - focused and have a strong sense of duty. They could start off as rivals, each thinking their way of fighting is superior, but then come to respect each other after facing a common enemy like the forces of Chaos.
Natsu and Akeno could have some fun interactions. Akeno has her own brand of mischief, and Natsu might not be used to her teasing ways. Their first meeting could be full of misunderstandings, with Natsu thinking she's an enemy at first because of her devious appearance, but then realizing she's an ally and developing an interesting friendship.
Naruto and Issei would be really interesting. Naruto, with his positive and determined attitude, would contrast with Issei's more pervy and hot - blooded nature. They could learn a lot from each other. Another interesting interaction could be Naruto and Sirzechs. Sirzechs, as a powerful devil king, would be intrigued by Naruto's power source, the Juubi. And Naruto would be interested in Sirzechs' leadership and power management in the devil world.
Itachi and Rias would be really interesting. Rias is used to being in control and having power, but Itachi's calm and collected nature along with his overwhelming power would put her in a different position. She would likely be intrigued by his Sharingan and his combat abilities. Itachi, on the other hand, would be dealing with a different kind of power structure and would have to navigate the social hierarchy of the devils in Highschool DxD.
Ben and Issei would be an interesting pairing. Ben is used to being a hero with his Omnitrix, and Issei has his own journey of becoming a powerful devil. They could learn from each other's combat styles. Ben could show Issei how to use his alien forms' unique abilities in battle, and Issei could teach Ben about the world of devils and the importance of relationships in his world.
Ichigo and Issei would be really interesting. Ichigo, with his calm and collected nature most of the time, compared to Issei's more pervy and hot - headed ways. Their different personalities could lead to some really funny and intense interactions, especially when it comes to fighting side by side or arguing about battle strategies.
Definitely Naruto and Issei. Issei is all about his perverted ways and getting stronger, while Naruto is focused on protecting his friends and achieving his dreams. Their clash of personalities would be really interesting. Naruto might not understand Issei's obsession with girls at first and try to set him straight. And Issei would be amazed by Naruto's power and want to learn from him.
One possible interesting plot could be that the Doom Slayer is somehow transported to the world of High School DxD. He could end up at the school as a new student, but his combat skills and his no - nonsense attitude would quickly set him apart. Maybe he gets involved in the battles between the different factions in the DxD world because they mistake his presence for a threat or an opportunity. He might use his arsenal of weapons from Doom to take on the devils, fallen angels and other supernatural beings in the DxD universe in his own unique way.
Blake could be a very interesting character in a RWBY Doom crossover fanfiction. Her ability to create illusions and her cat - like reflexes could give her an edge in the Doom universe. Also, her complex backstory and her more reserved nature compared to some of the other RWBY characters would make for an interesting dynamic when interacting with the Doom Slayer and the other denizens of the Doom world. She might be able to use her stealth to sneak up on demons or create illusions to distract them while the others attack from different angles.