For Ceasarion, his character could be developed by showing his growth from a young and somewhat naive heir to a more confident leader. He could learn from Titus Pullo's street - smart and battle - hardened ways. For example, Pullo could teach him how to read the intentions of people just by their body language in a fight or a political situation.
One idea could be a story where Ceasarion and Titus Pullo are on a quest to uncover a hidden treasure. They face various challenges along the way, like dealing with bandits and solving ancient riddles.
For Sakura, her character can be developed by showing her growth in dealing with someone as unpredictable as Hidan. She could start off being cautious and a bit scared of him due to his violent nature. But as the story progresses, she could become more confident in handling him. For Hidan, his character can be developed by having him question his own beliefs when interacting with Sakura. Maybe her scientific approach to things makes him think about his religious fanaticism in a new light.
They can be developed through facing challenges. For example, if they encounter a difficult puzzle or enemy, they have to use their wits and skills. This shows their growth.
For Rex, you could develop his character by showing his more vulnerable side when he's around Breach. Maybe he's usually the tough leader, but with Breach, he allows himself to show his doubts and fears. For Breach, show how he matures through his interactions with Rex. For example, he could become more responsible.
Pacman could be developed by showing his vulnerability. Usually seen as a strong and fast dot - eater, in the fanfic, he could be in situations where he's not so confident. For example, when facing a new kind of threat in Pinky's world. Pinky, on the other hand, could be developed by showing her kindness. We usually see her as a chaser, but here she could be shown as a protector, protecting Pacman from other threats in the game world.
Boruto could be developed by exploring his insecurities. He's often seen as a confident character, but in a fanfic with Sarada, he might have insecurities about being good enough for her or protecting her. By facing these insecurities and overcoming them, he grows as a character. Sarada, on the other hand, can be developed through her relationship with Boruto in terms of her loyalty. As they face challenges together, her loyalty to Boruto can be tested and strengthened, which also shows her character growth.
For Rukia, her character could be developed by showing her learning new skills or techniques from Sode no Shirayuki. This would not only make her stronger physically but also show her growth in terms of her adaptability. For Sode no Shirayuki, we could see her develop more of an emotional side as she spends time with Rukia. Maybe she starts to understand human emotions better.
To develop Sasuke, explore his relationships with other characters besides Sakura, like his old friends from the village. This would give more depth to his character. For Sakura, have her face some tough moral dilemmas that force her to make difficult decisions. This would show her growth and maturity. Also, show their relationship evolving over time through small, everyday interactions as well as big, life - changing events.
For Error, you could develop his character by showing his softer side when he's around Ink. Maybe he starts to care more about the things Ink creates instead of just wanting to destroy them. As for Ink, he could become more understanding of Error's glitches and not just see him as a nuisance. The lemon could be a factor in this development. For example, if the lemon has some sort of calming effect on Error, Ink could use that to his advantage to get closer to Error.
For Snivy, you can show its growth from being a bit naive to more confident. For example, at the start, it might be hesitant in battles, but as the story progresses, it becomes bolder. Servine can be developed as a more mysterious character at first, with its past gradually being revealed as it gets closer to Snivy.