A great plot twist could be that Raven is actually working undercover for a good cause all along, and Qrow discovers this in the middle of a fight against her. He thought she was a villain, but in reality, she was trying to stop a greater evil from within the enemy's ranks.
Another plot twist could be that a powerful force is controlling Raven's actions without her knowledge. Qrow discovers this and has to find a way to break the control. This would add a layer of mystery and urgency to the story, as Qrow not only has to save his sister but also figure out who or what is behind the mind control.
A more emotional fanfiction could be about Qrow trying to understand Raven's decision to leave. He could be on a journey of self - discovery as he tries to come to terms with his sister's actions. He might visit the places they used to go together, reminiscing about the good times and trying to figure out where it all went wrong.
One plot idea could be a gender - swapped Qrow in an alternate universe where she is a mentor to a new group of young hunters. She could have different relationships with the other characters, like a more motherly bond with Ruby. Another idea is that she is on a mission to uncover a conspiracy within the Huntsman academies, using her unique skills and charm.
One plot idea could be Qrow training Ruby in some special combat techniques that are unique to his own fighting style. This would allow Ruby to gain new skills and also strengthen their bond as family members.
Perhaps a plot twist would be that during the fight, Tai discovers a secret about Raven that completely changes his perception of her. For example, he finds out that she has been working undercover to stop a greater threat all along, and their fight then turns into a reluctant alliance against a common enemy.
A great plot twist would be if Raven is kidnapped and taken to a place where she meets her long - lost family members, but they're the ones who kidnapped her because they need her help to fight against a common enemy, and they knew this was the only way to get her attention. Another plot twist could be that the kidnapper has a split personality, and one side is good and wants to free Raven, while the other side is evil and wants to keep her captive. And the last plot twist might be that Raven is kidnapped into a parallel universe where everything is different, and she has to find a way back while also dealing with the kidnapper in this strange new world.
A good plot twist could be that Jinx is actually working undercover to protect Raven all along. Everyone thinks Jinx is out to get Raven, but in reality, she has been secretly guarding her from a greater threat that neither of them were aware of initially.
One idea could be Qrow having to protect an endangered species all on his own. Maybe he discovers a unique Grimm - like creature that is on the verge of extinction and he has to fend off other threats while trying to understand it. Another could be that Qrow is part of a mission to save a group of people who are considered 'endangered species' in the RWBY world due to some new threat, and he has to use his skills and experience to lead them to safety.
One interesting Uncle Qrow fanfic could be those that explore his relationship with Ruby. For example, a fanfic might focus on how he trains Ruby in secret combat techniques, adding more depth to their family bond.
A plot twist could be that the pregnancy is not what it seems. Maybe it's an illusion created by a villain to distract them from a bigger threat. Raven and Damian might initially believe it's real and start making all these plans, only to find out later that they've been tricked.
A good plot twist could be that Eve is actually a Nasod prototype with a hidden directive that makes her turn against Raven and their friends. Raven has to fight her, but also tries to find a way to reverse the directive without harming her.