Create relationships between the characters. Maybe there are two crew members who have a love - hate relationship. As the story progresses, this relationship can evolve. They could start off arguing but then come to rely on each other during a crisis in the Titan submarine, which would show growth and development in both characters.
Ymir's character could be developed by exploring her past more deeply. For example, her time as a Titan before joining the Survey Corps. This could make her more complex as she struggles with her identity. Christa, on the other hand, might develop by breaking out of her 'nice girl' persona. As she faces more challenges with Ymir by her side, she could become stronger and more assertive.
A survival - themed plot could be interesting. For example, the Titan submarine could get stranded in an unexplored part of the ocean. The crew then has to deal with limited resources, strange underwater phenomena, and their own internal conflicts as they try to find a way to be rescued.
For Jean, show his growth from being a somewhat self - centered guy to someone who truly cares for the OC. Highlight his leadership skills in battle and how he uses them to protect the OC. For the OC, give her a distinct personality. If she's shy, show how she overcomes that around Jean. If she's brave, show how she inspires Jean.
The character can start as a normal person who suddenly discovers their Titan connection. They should have flaws like being overly impulsive or having a fear of their newfound powers. As they interact with the Percy Jackson world, they learn from their mistakes and grow. For example, if they're too impulsive and it gets them into trouble with a monster, they'll learn to be more cautious. They can also develop relationships, like a mentor - mentee relationship with an older demigod who helps them understand their Titan side.
Writers can give the Female Titan more depth by exploring her emotions. Even though she is a Titan, she can still feel things like anger, fear, or regret. For example, showing her hesitation before attacking a particular character can make her more interesting.
Communication is key. They can start by simply talking about their daily tasks and experiences in the Destiny universe. For example, the Titan female can share stories about her battles on the front lines, and the Warlock female can talk about her research in the tower. This can lead to a deeper understanding of each other.
Percy could be developed by facing moral dilemmas. For example, when dealing with the eldest Titan, he has to decide whether to trust this ancient and powerful being. This forces him to grow and think more deeply about right and wrong.
For Adanna, you could develop her character by giving her a backstory. Maybe she had a difficult childhood that made her strong - willed but also a bit guarded. As the story progresses, she could learn to open up more, especially to Aoi. For Aoi, you could show his growth in terms of responsibility. If he starts as a carefree character, put him in situations where he has to take charge. This will make his character more multi - dimensional.
For Percy, you could explore his insecurities more deeply. Maybe he's worried about living up to his reputation as a hero. With Emma, give her unique traits. For example, she could be really good at deciphering ancient languages. Then, put them in situations where they have to rely on each other. Like when they're trapped in an ancient maze.
A female character could be developed as a Dalek sympathizer. This would be an interesting twist. She might believe that the Daleks are not entirely evil and that there is a way to rehabilitate them. She could work towards that goal in the fanfiction, facing opposition from other characters who see the Daleks as pure evil.