The OC could start as an adversary to Tsuna. Maybe the OC initially misunderstands Tsuna's intentions and sees him as a threat to the balance of the Arcobaleno world. But as time passes, they realize Tsuna's good heart and start to work with him.
When it comes to the other Arcobaleno members, the OC could offer a fresh perspective. For example, with Fon, the OC could exchange ideas about different fighting styles that are related to their respective powers. The OC could also form a friendship with Lambo, perhaps protecting him from danger and in return, Lambo could introduce the OC to some of the more fun aspects of the Reborn world that they may have overlooked.
One idea could be that the OC has a special power related to the sky that no one expected. For example, they can manipulate the air in ways that are not typical for the Arcobaleno powers. Maybe they can create solid air constructs that can be used for defense or offense.
First, you need to have a clear understanding of the Sky Arcobaleno concept in the original work. Research their powers, characteristics, and the world they exist in. Then, create a well - developed OC with a unique personality and backstory. Make sure their story fits within the existing lore but also adds something new.
First, create a detailed profile for your OC. Decide on their appearance, personality, and backstory. Then, think about how they fit into the arcobaleno world. For example, are they a new addition to the group or a replacement for an existing character? After that, come up with a basic plot idea, like a mission they have to go on or a problem they need to solve.
One interesting story could be about an OC who discovers a hidden power within the Sky Arcobaleno heritage and has to learn to control it while facing various challenges from other Arcobaleno. It might involve a journey of self - discovery and making unexpected alliances.
Obviously, the oc reborn as Issei would interact with Rias Gremory. She is a central character in the High School DxD world and as Issei is part of her peerage, the oc in Issei's place would have a lot of interaction with her. This could range from her guiding the oc in the ways of the devils to them having some sort of romantic or at least a very close friendship relationship.
Since I don't have specific information about this fanfiction, I can't say for sure who the main characters are. But they are likely to be the original characters (OCs) created for the 'Reborn's Sky' universe.
Well, you could base your 'new sky arcobaleno oc fanfiction' on a time - travel concept. Have your OC travel back in time to the origin of the arcobaleno and change certain events. This would not only create a complex and engaging plot but also allow for a lot of character development. Or perhaps make the OC a healer, using their sky - related powers to heal not just physical wounds but also emotional traumas of the other characters. This would give a fresh perspective on the arcobaleno world.
Sasuke is also a likely candidate. The OC could try to understand Sasuke's pain and help him find a different path than revenge. Their interactions could be full of tension and deep conversations about power, family, and loyalty.
The Wood Style OC could be a rival to Naruto. Since Naruto has the power of the Nine - Tails, the OC with Wood Style could see Naruto as a threat to their own status as a powerful ninja. This would lead to intense battles and a begrudging respect as they learn more about each other's abilities and motives.
OCs can interact with the main characters in various ways. They could be classmates at Hogwarts. For instance, sitting next to Harry in Potions class and having a friendly rivalry or a helpful partnership.