I'm Female Lead In Their World: Living in the High School of the Dead

"Thank God, there are no undead on this floor," Okada muttered, trailing behind the group of seniors.
As they reached the staircase, they spotted a small group of undead—three or four, shuffling aimlessly. Takashi immediately took charge, leading the team forward. Rei, Hisashi, and Saeko flanked him, effortlessly clearing the path of danger, their movements synchronized as though they had been training for this all along.
Niikaz stayed close to Kazu, who was clutching a box filled with bread. Her eyes scanned the area, always on the lookout for danger. Her hands never left her custom-made weapon, ready to pull the trigger at a moment's notice. Each of her shots was swift and silent, dropping any undead that came too close to Kazu without drawing attention to herself.
"Where's the closest shortcut?" Takashi asked as they moved forward.
"The front door leads straight to the parking lot," Takagi replied, pointing toward a narrow bridge that connected them to the next building. "We can cross it after that!"
Without hesitation, Takashi gave orders. "Rei, Hisashi!"
"On it!" they replied in unison, quickly opening the large doors that led to the bridge. Takashi and Saeko immediately engaged the undead on the other side, with Saeko's wooden sword cracking against skulls and Takashi dealing deadly blows with his weapon.
"This place seems relatively empty," Saeko observed as they moved through the area. "We should avoid unnecessary fights."
"Yeah," Takashi agreed, glancing around. The others nodded silently, but before they could get comfortable, undead began spilling out from the shadows of the adjacent building.
Hirano took his position next to Takagi, expertly reloading his nail gun as he fired at the approaching undead. He kept an eye on her, protecting her while maintaining their distance from the danger.
On the left, Okada assisted Saeko in clearing the undead, while on the right, Rei and Hirano worked to keep the enemies away. At the center, Marikawa and Takagi struggled to keep up with the pace, but they were determined not to be left behind.
Kazu, holding tightly to the box of bread, did his best to avoid combat altogether, staying behind the group and focusing on keeping his balance while dodging any potential threats. His movements were cautious and careful, his grip on the supplies never loosening despite the chaos.
Niikaz remained at the back, silently taking out any undead that got too close, her unique weapon making her an invisible guardian. Her gun never made a sound, and her shots left no trace, allowing her to operate without drawing attention from the group—or the undead.
As they reached the bridge, Niikaz glanced over her shoulder, noticing that more undead had started to follow them. The shambling horde was slow but persistent, and if they didn't act fast, they would be overwhelmed.
(Seems like I'll need to use that this time…) she thought, vanishing her gun from sight and bringing her palms together. A faint glow began to form between her hands, creating a small orb of energy.
"Niikaz, what are you doing?" Kazu, who had fallen behind, noticed Niikaz was no longer moving with the group. He hurried over to her, still holding the box of bread awkwardly in his arms.
"Don't worry, this won't make any noise," Niikaz said with a smirk, showing him the small black orb that now floated above her hands. The object resembled a miniature planet, with thin rings orbiting it like Saturn.
Kazu blinked in disbelief. "Am I dreaming?" he muttered to himself with force smile, struggling to comprehend what he was seeing. As if the chaos of the undead wasn't enough, now Niikaz was creating glowing orbs out of nowhere?
His mind reeled. He tried to process the situation, but it all felt surreal. He stood there, mouth slightly open, too shocked to even form a coherent thought.
"No, you're not dreaming," Niikaz said flatly, flicking his forehead with her finger. The sudden touch snapped him out of his daze.
"Ouch," Kazu muttered, more surprised than hurt. He blinked a few times, refocusing. "What is that thing? In your hands?"
"A bomb," Niikaz answered casually.
"Ooo- Is A bomb…?" Kazu nodded slowly, his mind still catching up.
Then, all at once, the realization hit him. "Wait, what?! A BOMB?!"
His face drained of color. Sweat began to pour down his temples as panic set in. "That's a bomb?! What are you thinking? That's too dangerous! What if it attracts more of them?!"
Niikaz giggled. "Relax, just watch," she replied calmly. With a flick of her finger, she sent the bomb flying toward the horde that had been creeping up on them. Kazu flinched, expecting a loud explosion, but to his surprise, there was nothing.
The bomb landed silently among the undead. A moment later, a wave of sharp needles shot out from the orb, piercing the bodies of the undead with precision. Kazu gasped as the creatures collapsed, each one dropping like a puppet whose strings had been cut. The entire group of undead had been eliminated in seconds, yet there hadn't been a single sound to give them away.
"W-woah…" Kazu stammered, still in shock. "That… that was amazing. I didn't hear a thing."
"Told you," Niikaz said proudly, her tone casual as if she hadn't just wiped out a small horde of undead. She quickly caught up with the others, acting like nothing had happened.
By the time Takashi's group finished dealing with the undead in front of them, Niikaz and Kazu had rejoined the group, and the two of them moved forward as if nothing out of the ordinary had occurred.
"You guys are late," Takashi said, glancing over his shoulder. "Hisashi was about to come up to check on you."
"Sorry, stuff happened," Niikaz replied with a casual shrug, keeping the details to herself.
As they descended the stairs to the first floor, the group came to a sudden halt. Below them, hundreds of undead swarmed the ground floor, filling every inch of space with their rotting bodies.
Kazu clutched the box of bread even tighter, knowing that losing their supplies would be disastrous. He stayed close to the back of the group, ensuring that the food remained safe while Niikaz stood beside him, ready to protect him if needed.
Niikaz scanned the room, her sharp eyes picking up on the subtle differences in the scene compared to the original story she knew. In the original timeline, another student should have been with Takuzo's group, the one responsible for making noise that nearly got them all killed. But now, that student was nowhere to be found.
(Hmm, looks like my presence is changing events…) Niikaz thought, her mind racing. (I'll have to be careful. This world is adapting, and I need to stay one step ahead.)
"Hey, you guys good back there?" Takashi called out, his voice snapping Niikaz back to the present.
"Yeah, we're fine," she answered casually.
"Y-yes! We are fine , Takashi-Senpai" Kazu staring at Takashi masking his unease. "Let's keep moving."
With the path forward blocked by the undead horde, and the uncertainty of what lay outside, the group prepared for their toughest challenge yet.