For Pacman, his character can grow by learning about Pinky's perspective. He might start to understand why Pinky chases him all the time. This could lead to him being more empathetic. Pinky could be developed by having her face internal conflict. Maybe she starts to question her role as a chaser when she gets to know Pacman better. She could struggle between her natural instinct to chase and her new - found friendship with Pacman.
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.
One possible plot could be that there is a magical event that causes Pacman and Pinky to swap abilities. Pacman now has Pinky's speed and stealth, and Pinky has Pacman's ability to eat dots. This leads to a lot of chaos and confusion at first, but eventually, they learn to use their new abilities together to solve a bigger problem in the game world, like a new enemy that neither of them could face alone.
One possible plot could be that Pinky has always been curious about the outside world of the Pac - Man maze. One day, a strange lemon - scented portal appears. Pinky, being the adventurous one, enters it and ends up in a different dimension. Pacman, noticing Pinky's disappearance, follows him. In this new world, they discover that the lemon - scented environment is slowly affecting their abilities. They must find a way to reverse this effect and also figure out how to get back to their own world while dealing with the unique challenges of this lemon - fanfiction world.
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.
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.
It could be a giant lemon - themed monster that wants to turn the Pac - Man world into a lemon - only place. This monster might be jealous of Pacman's popularity and sees the lemon - themed transformation as a way to make everything his own.
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.
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 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 Divine, you could start by exploring their backstory. Maybe they come from a long line of magic - users but have a unique power that sets them apart. This could lead to internal struggles as they try to master this power. For Legeater, perhaps focus on their physical abilities and how they got them. Were they trained by a master? Or did they develop them through self - discipline?
To develop the characters in a 'naegi x harem fanfic', consider their backstories. If one of the female characters had a difficult past, it can shape how she approaches Naegi and the other harem members. Also, let their relationships with Naegi evolve over time. Maybe at first they're just friends, but as they face challenges together, their feelings change. You can also use dialogue to show their growth. For example, a character who was initially quiet starts to speak up more as she becomes more confident in her relationship with Naegi.