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.
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.
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.
Chapter 117, "Caught In A Pinch I", is the clearest early answer because it turns Narna's situation into a concrete plot event. It opens with A brilliant flash of light illuminated the dense foliage as a magic... and closes on He stared into the distance, his mind already calculating the day's.... The key payoff is that the chapter closes with Keith remained calm, his blade glinting as he watched the battle unfold.
Chapter 174, "Closing The Cave", is the clearest early answer because it turns Damien's situation into a concrete plot event. The setup is The fifth tunnel loomed ahead, dark and unyielding., but the pressure keeps building through Damien entered cautiously, his summons flanking him as the faint....
Chapter 490, ", I Became an Investor of Assassin Court?", is the clearest early answer because it turns Assassin Court's situation into a concrete plot event. The setup is Thirdly, I too am outraged by what Norberto has done., but the pressure keeps building through If you need any help, just say the word..
Chapter 488, ", Gambling with Your Life", is the clearest early answer because it turns Interstellar Warriors's situation into a concrete plot event. The setup is The representative of the Interstellar Warriors is usually a Battle..., but the pressure keeps building through The current representative is Jerry Earl Ganglong, the Battle Group....
Chapter 71, "Visit To The Elderglow Academy I", is the clearest early answer because it turns Elderglow Academy's situation into a concrete plot event. The setup is The meeting had ended after their agreement on the nominations as..., but the pressure keeps building through They were yet to discuss which representative would go to which....
Chapter 121, "Damien's Arrival", is the clearest early answer because it turns Obsidian Drake's situation into a concrete plot event. It opens with Damien moved cautiously through the dense forest, his steps measured... and closes on Attack it!" she commanded, pointing at the Obsidian Drake..
Chapter 46, "Actively Hunting III", is the clearest early answer because it turns Tree Demons's situation into a concrete plot event. The chapter turns that into something concrete by moving from It only took a second for a vine to slam into Damien and send him... to The first one arrived from his front in a slow sweep and Damien slid.... What makes it stick is that the chapter closes with "Huh?" This one had a scarier auram one that Damien had only felt from one beast.
Chapter 73, "Visit To The Elderglow Academy III", is the clearest early answer because it turns Dean Godsthorn's situation into a concrete plot event. It opens with Standing in the middle of the teleportation array within a certain... and closes on Woonng~ The humming continued for a few seconds before finally dying.... The key payoff is that the chapter closes with Lord Acheon nodded at the response and then he spoke.
Chapter 254, "The Beast Tamer Town", is the clearest early answer because it turns Damien's situation into a concrete plot event. The chapter turns that into something concrete by moving from Damien walked through the town's winding streets, following Lizella... to On the other hand—it also meant that if a beast betrayed its tamer,.... What makes it stick is that the chapter closes with Now that was unexpected. "Uhm...
Chapter 21, "The Unaccounted Incident", is the clearest early answer because it turns Jack's situation into a concrete plot event. The setup is At first, it seemed like a large drop of blood floating in the air,..., but the pressure keeps building through They had fought demons before—battled unimaginable forces—but this....