There could be a fanfic where Blake and Mark are the only two survivors of a major attack by Salem's forces. They then have to rely on each other completely to survive and rebuild. This plot would be unique as it would focus on their survival skills and how they grow closer in such a desperate situation. It could also show how they come up with new strategies to fight back against Salem using their combined strengths.
I'm not sure of a specific one named 'Blake Mark RWBY fanfic' with a truly unique plot off the top of my head. But a fanfic that could be unique might be one where Mark has a special power that he uses to help Blake in a completely unexpected way. For example, he might be able to communicate with Grimm in a certain sense and use that to their advantage in battles.
A potentially unique Blake Mark RWBY fanfic could be one where Mark is from a different dimension entirely. He gets sucked into the RWBY universe and meets Blake. Their story could revolve around him trying to find a way back home while also helping Blake with her own problems. This would introduce a whole new set of dynamics and challenges, as Mark has no prior knowledge of the RWBY world and has to learn quickly.
Chapter 357, ", Meat Mountain", is the clearest early answer because it turns Gu Hang's situation into a concrete plot event. The chapter turns that into something concrete by moving from He didn't count on a cloud of poisonous fog to completely seal off... to Next, its current state was astonishing—it was trembling, convulsing..
Chapter 433, ", Subversive Action", is the clearest early answer because it turns Planetary Government's situation into a concrete plot event. The chapter gives readers a real answer by opening on The overall plan seems plausible, and the chances of success appear... and ending on First was the annoyance from the troublemakers..
Chapter 281, ", Torn to Pieces", is the clearest early answer because it turns Wind Falcon's situation into a concrete plot event. Early on, Irong Fetches would never be caught 'off guard'.. By the end, The situation had to be resolved quickly and could not be delayed any.... Inside the broader technology upgrade storyline, the chapter closes with He didn't know how to respond., which gives Wind Falcon a stronger narrative position and pushes the power growth onward.
Chapter 365, ", A Million Kindness", is the clearest early answer because it turns Great Demon's situation into a concrete plot event. It opens with Though their combat strength was fierce, and they played a... and closes on Fino City may have been destroyed, but the Plague Demon Army that....
Chapter 472, ", Straight to the Heart", is the clearest early answer because it turns Green Skins's situation into a concrete plot event. The setup is A Green Skin youngster could either climb higher in this endless..., but the pressure keeps building through This also led to a situation where once an area became completely....
Chapter 283, ", The Mystery of the Gene Seed", is the clearest early answer because it turns Phoenix's situation into a concrete plot event. The chapter turns that into something concrete by moving from Rebirth?" Gu Hang frowned, quite puzzled. to But their genetic origins were the same..
Chapter 273, ", Sun Lord (6k additional)", is the clearest early answer because it turns Rage Owl Star's situation into a concrete plot event. The setup is Now, Gu Hang has exposed a scandal about Blackbird Heavy Industries..., but the pressure keeps building through Or, in order to clear themselves of the connection, might they....
Chapter 392, ", Economic Reform and Development Plan", is the clearest early answer because it turns Alliance's situation into a concrete plot event. The chapter turns that into something concrete by moving from Lowering the rating by one level means innumerable benefits; the... to Highly skilled technicians in the factories, important management....
Chapter 339, ", Fine Gold, Knight and Titan", is the clearest early answer because it turns Gu Hang's situation into a concrete plot event. Early on, A thousand-tier draw, though not drained dry, left hardly anything.... By the end, It is a technology developed to compete with the Interstellar Warrior....
Chapter 429, ", Battle Moon", is the clearest early answer because the buildup finally cashes out in a real clash. The chapter turns that into something concrete by moving from The Planetary Defense Force of Frost Origin IV had been consolidated;... to They had tried their hardest, but the real differences made the.... What makes it stick is that the danger stops being abstract and the conflict around Green Skin becomes immediate, forcing the surrounding cast to react under pressure.