One possible fanfiction could be about Sentinel Prime and Optimus Prime having to work together to save Cybertron from a new, powerful enemy. They might start off with some differences in their approaches but gradually learn to combine their strengths.
There isn't really a clearly defined and traditional 'love story' between Optimus Prime and Arcee in the original Transformers lore in a very romantic sense. They are comrades in arms. They fight side by side for the same goals, to protect their planet and their kind. Their relationship is more about mutual respect and a shared sense of duty.
Baby Optimus Prime's character can be developed by exploring his relationships. If he has a mentor figure among the Autobots, his interactions with that character can shape him. He might look up to this mentor and try to imitate their good qualities. His relationship with other baby Transformers or younglings can also be important. He could learn about sharing, cooperation, and friendship through these relationships. Additionally, his discovery of his own strength, both physical and mental, can be a key part of his development. For instance, when he first realizes he can lift a small object that others thought was too heavy for him, it gives him confidence.
The other characters in the Highschool DxD world would have a wide range of reactions. The angels might see Optimus as an unknown factor and be a bit suspicious. The fallen angels might try to manipulate the situation to their advantage. And the normal human students would be terrified at first. But as the story unfolds and they see Optimus Prime's noble actions, they could start to look up to him as a hero, much like how the Autobots are seen as heroes in their own universe.
In the official Transformers lore, there is no canonical love story between Arcee and Optimus Prime. Their relationship is mainly based on comradeship within the Autobot ranks. They are both focused on the greater mission of protecting Cybertron and the universe from the Decepticons.
One great fanfiction could be 'The Bond Beyond Bots' which explores their relationship in a post - apocalyptic world. It shows their deep connection and how they support each other through tough times.
There are many great Optimus Prime and Arcee love fanfictions out there. One popular one might explore their relationship during a time of great battle, where their love becomes a source of strength. Another could be a more in - depth look at how they first fell in love, perhaps during a moment of peace on Cybertron.
A plot could be that Optimus Prime, in his travels, discovers a lost civilization. There, he meets a female leader who is intelligent and kind. She is intrigued by his noble nature, and he by her leadership and the unique culture of her people. As he helps her protect her civilization from various threats, their relationship blossoms into love.
In such a fanfiction, Naruto could be fascinated by Optimus Prime's technology. He might try to find ways to incorporate some of the Autobot's tech into his ninja tools. Maybe he'd develop a new type of shuriken that has some of the functions of Optimus' weapons. Also, Naruto could learn about the concept of a team from Optimus, where every member has a role to play, and apply it to his own ninja team dynamics.
In a fanfiction, Ratchet and Optimus could be sent on a secret mission. They are alone, away from the rest of the Autobots. This gives them a chance to have more personal conversations. They might discuss their hopes for the future of Cybertron, their fears about the Decepticons, and their memories of the old days. The story could show how they support each other not just in battle, but also on an emotional level.