Yang from RWBY would be another interesting choice. Her fiery personality and powerful punches could bring a different kind of energy to the Halo Wars universe. She might get into some interesting battles with the Covenant, using her brute strength and her Semblance of absorbing damage to become even stronger in combat.
Ruby could be really interesting. Her naivete and pure - hearted nature would contrast with the often - cynical and war - torn world of the Clone Wars. She could inspire the clones and Jedi with her unwavering belief in doing good, and her scythe - wielding skills would be a unique addition to the battles.
I think Weiss could be the most interesting. Her strict upbringing and refined combat style from RWBY would contrast greatly with the rough - and - tumble nature of the Halo universe. She might struggle at first to adapt but then use her intelligence and Glyph - based powers to come up with some really cool strategies against the Halo enemies.
Sasuke would be really interesting. His brooding nature and thirst for power could lead to some complex storylines in the Halo universe. He might be intrigued by the Forerunner technology and seek to use it for his own ends.
Mercury from RWBY could be an interesting character to focus on. He has a rather morally ambiguous nature already. In a Darkwatch fanfiction, he could be tempted by the power of the Darkwatch's enemies, like the vampires or demons. His prosthetic legs could also be given some kind of dark upgrade, and we could see him struggle between his own self - interest and the greater good in this new and dangerous setting.
Ruby would be really interesting. Her optimism and determination in RWBY could be a great contrast to the often dark and foreboding nature of the Dark Tower universe. She could inspire the characters there with her can - do attitude and also learn a lot from the more cynical or world - weary characters in the Dark Tower world.
Ruby. She has that innocent and curious nature which would make her reactions in the SAO world really interesting. She could be fascinated by the virtual world and its different rules, and her positive attitude might be a source of hope for the other characters. Also, her scythe - using skills could be adapted in the SAO combat scenarios in unique ways.
Ruby would be really interesting. Her energetic and optimistic nature would contrast greatly with the often dark and power - hungry characters in the Overlord world. She could inspire some of the downtrodden minions with her belief in the good of people. Also, her scythe skills and speed would be a unique addition to the battles in the Overlord universe.
I think Blake would also be a great focus. Her stealth and agility would translate well in the Monster Hunter world. Plus, her cat - like Faunus traits could give her an edge in certain situations, like tracking or sneaking up on monsters.
One of the most interesting combinations could be the Prophet of Truth from Halo and Emperor Palpatine. Both are power - hungry and manipulative leaders. Their encounter could be a battle of wits as they try to outmaneuver each other. And what about Spartan Locke and Rey? Locke's skills as a Spartan and Rey's emerging Jedi powers could result in a great partnership. They could train together and learn from each other's different combat styles.
Ruby and Master Chief could be a great pairing. Ruby's enthusiasm and quick - thinking could complement Master Chief's stoic and strategic nature. They could learn from each other's combat styles and leadership skills during battles against the combined threats of Grimm and Covenant.