Perhaps Cortana and Dr Halsey team up to train a new generation of Spartans. They could develop a new training program that combines Cortana's strategic knowledge and Dr Halsey's scientific expertise. Along the way, they face challenges from within the military establishment who are skeptical of their new approach, and they have to prove that their ideas are valid and beneficial for the future of humanity in the Halo world.
One plot idea could be that Cortana and Dr Halsey work together to solve a mystery within the Halo universe. Maybe there's a malfunction in some ancient Forerunner technology that they need to figure out before it causes chaos. They could use their combined knowledge of AI and scientific research to crack the problem.
A plot could involve Dr Halsey teaching Cortana about human emotions and how they can be useful in making decisions, even for an AI. This could lead to Cortana having a deeper understanding of the human element in the battles and situations they face in the Halo universe. It would be a character - building exploration for both of them.
Appropriateness is subjective to some extent. Some people might find any fanfiction involving these characters acceptable as long as it is well - written and shows an understanding of the characters. Others might be more strict and only consider it appropriate if it strictly follows the 'canon' of the Halo series and doesn't deviate into areas that might seem out of character or inappropriate for the franchise.
One plot idea could be Cortana getting trapped in a virtual reality world created by a rogue AI. She has to fight her way through various digital obstacles and enemies while trying to find a way back to the real world. Another idea is that Cortana discovers a long - lost part of her code that gives her new abilities and she uses these to protect humanity from a new threat. Maybe Cortana could also time - travel to different points in the Halo universe's history and change certain events to save more lives.
One idea could be a Cortana crossover with the Halo universe and Star Wars. Cortana could interact with droids in the Star Wars galaxy, sharing her advanced AI knowledge. Another could be a crossover with the Mass Effect series, where Cortana aids in the fight against the Reapers. Maybe she could also cross over with the Transformers universe, helping the Autobots with strategic planning using her computational skills.
One idea could be a crossover where the characters from RWBY end up in the Halo universe. They might team up with John and Cortana to fight a common enemy, like a new type of Grimm that has somehow made its way into the Halo world. Another plot could involve the sharing of technology or powers between the two groups. For example, Ruby's scythe skills could be combined with John's combat training to create a unique fighting style.
One idea could be a crossover with the Justice League. Dr Fate could use his magic to help the League against a powerful magical threat that they can't handle alone. Maybe a dark sorcerer from another dimension is trying to invade Earth, and Dr Fate's knowledge of ancient magic is crucial in devising a counter - attack.
A possible plot could be that there are complications with her pregnancy. This leads to a journey to find a specialist or a special medicine. Along the way, she meets old friends and foes, and through her determination and the support of her loved ones, she overcomes the difficulties and looks forward to the birth of her baby.
Maybe a plot where Rose, who has her own experiences with the Doctor, and Martha, with her medical knowledge, find a strange alien illness spreading on Earth. They need to figure out its origin and how to stop it while also dealing with their feelings about the Doctor. For example, Rose might be a bit jealous of Martha's time with the Doctor, but they have to put that aside for the greater good.
One idea could be that they team up to solve a mystery in their city. Maybe there's a series of strange disappearances and their combined skills, Hawkodile's strength and Dr Fox's intelligence, are needed to figure it out.
One idea could be a what - if scenario. What if Strange and Christine had a moment of passion during a time - traveling adventure? Maybe they kiss in a parallel universe where they're not bound by the normal rules of their relationship in the main MCU timeline.
One idea could be exploring Mr Hyde's backstory in more detail. Maybe he had a tragic childhood that led to his dark nature. Another could be a scenario where Dr Jekyll tries to find a permanent cure for his transformation into Hyde but faces many obstacles. A third idea might be a love interest for Mr Hyde that could potentially change him.