It's possible that some of the villains from RWBY could also be main characters in this fanfic, especially if they are after the ancient bomb. For instance, Cinder Fall or Salem might be interested in the power of the ancient bomb and be the main antagonists in the story. Their actions and the heroes' responses to them would then form the core of the plot.
I'm not sure as it depends on the author of the fanfic. But it could be the main RWBY characters like Ruby, Weiss, Blake, and Yang. They are often the central figures in RWBY - related stories, so they might be the ones dealing with the ancient bomb.
Since it's a fanfic, the author could introduce new characters specifically for this story about the ancient bomb. Maybe there's an old sage - type character who knows the secrets of the ancient bomb and guides the main RWBY characters. Or there could be a group of treasure hunters who accidentally stumble upon the bomb and then have to deal with the consequences, and they could become important characters in the fanfic.
Chapter 107, "The Great Peril on the North Slope of the Cliff [3-in-1 Mega Chapter]", is the clearest early answer because it turns Great Xia's situation into a concrete plot event. The chapter turns that into something concrete by moving from But speaking of it, just how big is Redwood Ridge..." That thought... to The world's dangers didn't only stem from deceitful monsters; who....
Chapter 427, "Another Tunnel", 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 The echoes of battle had faded, leaving only the faint drip of water... to What about him?" Damien didn't answer immediately.. What makes it stick is that the chapter closes with The night air offered no reply., which gives the main cast a stronger narrative position and pushes the faction conflict onward.
Chapter 480, "New Variants", 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 There was no dramatic punch, no drawn-out conflict. to But several others were the variants he'd spoken about.. What makes it stick is that the chapter closes with "Disgusting things." He spat., which gives this chapter's turning point a stronger narrative position and pushes the power growth onward.
Chapter 115, "New Earth-digging Realm, Enhancing Mining Efficiency [Three in One]", is the clearest early answer because Xia Chuan finally turns buildup into a real advancement. A useful checkpoint is the way the scene starts with On the third day of moving into the new residence, on the second... and follows through with The new contribution system was meant to provide them a normal....
Chapter 144, "Self-serving at the Expense of Others, He Meng's Furious Rage [Sorry for Being Late]", is the clearest early answer because it turns Redwood Ridge's situation into a concrete plot event. The chapter turns that into something concrete by moving from Don't touch that Teng Jiao, it's poisonous!" "The Hunting Team's... to If they can, like tonight, reap three heads of prey without doing....
Chapter 486, "Helping A Village", is the clearest early answer because it turns Damien's situation into a concrete plot event. The chapter gives readers a real answer by opening on The village lay in a shallow basin between two low hills, its fields... and ending on A woman stepped out first, clutching a pitchfork with trembling hands..
Chapter 79, "Luo Ming's Mouth Shines Brightly", is the clearest early answer because it turns Li Baihe's situation into a concrete plot event. It opens with The distance between Great Xia and Rogel Camp is actually just four... and closes on For safety, Xia Hong shortened the length of the team as much as....
Chapter 386, "Orb Hunting", is the clearest early answer because it turns Razel's situation into a concrete plot event. The setup is The wind had picked up over the eastern centres as three of the..., but the pressure keeps building through Razel Acheon, sharp-eyed and steady-handed, unearthed another orb....
Chapter 415, "An Inside Attack", is the clearest early answer because the buildup finally cashes out in a real clash. It opens with Apnoch shook his head, a wry smile tugging at his lips. and closes on Understood, General." Damien, who had been hovering near the edge of.... The key payoff is that the chapter closes with It was inside of Delwig, the impregnable city., which gives this chapter's turning point a stronger narrative position and pushes the family politics onward.
Chapter 450, "Breaching The City", is the clearest early answer because it pushes Ivaan into a new phase or setting. The chapter gives readers a real answer by opening on The first thing Damien felt was pain. and ending on What is that thing?" one of the soldiers asked.. In story terms, the chapter closes with "IVAAN!" he roared, his voice echoing across the chaos., which gives the central conflict a stronger narrative position and pushes the faction conflict onward.