"So this thin hair-like stuff is going to turn into silver?" Chrome asked, brown eyes wide with incredulity as he stared at said object in his hand. "Damn...I thought they were some roots from some plant.

Both you and Suika let out a small noise of awe as Senku took the item from the other teen and dumped it into a clay pot before stirring its content the sharp end of the spear. Meanwhile, in the background, Kohaku was training the brothers as usual, but only the eldest of the two was focusing on the task at hand.

The youngest, on the other hand, was too excited with the prospect of finally getting a silver spear to pay much attention. The corners of his lips stretched into a wide smirk as Ginro raise his volume on purpose so that a specific somebody would hear him loud and clear. "That's going to become my silver spear, huh? Man, science sure is strange, isn't it? Speaking of which..."

At this point, both Kinro and Kohaku stopped their training as they turned to the blonde, his smugness growing with each word aimed at his brother. "Kinro, you already got your golden spear, rib—Oh, wait...Sorry! I didn't notice. Who would have thought we'd only get a silver spear, and not a gold one?"

A dark look fell over said brunette's face at his younger brother's mocking and tried to hold back from murdering his kin in cold blood, his hands curling into tight fists while he gritted his teeth.

Ginro's fun was interrupted by a harsh bark coming from a fuming Kohaku who had enough of his nonsense and sent the poor blonde flying backwards into a tree with a direct kick to his face. "Ginro, move your arms, not your mouth!"

Going back to the science group, none of you was paying attention to the commotion going on behind. As you watched Senku, a thought came to mind and you couldn't help but wondered, "Hang on, though. Why are you only making a sliver spear?"

"Because we need it to get the maximum danger materials," The green-haired scientist responded as he finished up on the spear, letting out a pleased hum at how it came out.

"Yes!" Ginro cried, tears of joy gushing out of his eyes like a waterfall as he admired his silver spear. "I finally have a silver spear!"

"You don't owe me one millimeter of thanks. I didn't make that for you." Senku said as he placed a bunch of glass jars into a bag before hauling it over his shoulder and glancing over his shoulders at the blonde with a mysterious smirk. "Come on, let's get moving. Ginro, your job is to be the team's bodyguard."

Upon hearing that, a satisfied expression appeared on said person's face as his eyes glimmered with exhilaration at thought of it. With that, all of you set off to the next place where science was waiting.

Time skipped

"Bodyguard! Bodyguard! I'm a bodyguard! I'm Ginro!" Ginro chanted with glee as he led the group to wherever Senku has in mind, each step filled with a light bounce that showcased his happiness.

Soon, all of you came across small pockets of hot springs and Kohaku couldn't help but commented, "Hey, this is the hot spring area that I draw hot water from all the time."

Chrome, who thought the group was going to be collecting hot spring water, turned to Senku with a small frown and said, "I came all prepared because you said it was going to be 'maximum danger'."

"Yea," You hummed in agreement. "How is hot spring dangerous? The most dangerous thing that we can do is scalding ourselves by accident."

"It gets dangerous up ahead." The scientist answered before barking at Ginro to stop playing around with his spear. "Ginro, quit messing around and hold your spear forward."

"Huh?" Said blonde responded in a confused tone as he stopped in his trek and stared at the other teen with wide eyes.

For once, there was no teasing or the usual confidence that Senku wore as he walked up to Ginro and held the spear so that it was pointing to the front while explaining in a serious voice. "This silver spear is a sensor. That's what I made it for. Take a good look at the tip. If that silver spear turns black..."

Looking down at the spear, Ginro saw his reflection staring back at him from the shiny surface as he muttered to himself – still not understanding where the scientist was going with this. "If it turns black...?"

A dark look fell over Senku's face as red eyes narrowed into a sharp glint, the corners of his mouth curling into a grim frown as he completed his sentence. "A few seconds later, you'll be dead."

Immediately, the joyful look fell from the blonde's expression as horror overtook his face, green eyes wide with startlement. He wasn't the only one reeling with shock over what the scientist said as the rest of you exchanged equal looks of confusion and concern.

"You need to get away within 0.1 seconds." The scientist told Ginro before directing his gaze towards everyone else, his expression remaining grave as he explained further. "We'll all run, too. The enemy we're about to go up against will send us to the afterlife with just one mistake. This is the greatest hurdle in making sulfa drugs."

The light mood from before was gone after hearing those words and you swallowed nervously as your heart sank to your stomach, feeling the severity of Senku's warning.

You weren't the only one feeling this way as the rest wore a similar expression on their faces, especially Ginro. No one wanted to advance further but for the sake of curing Ruri, they forged on with heavy hearts in each step.

As all of you approached closer to the destination, there were evident signs along the way that spoke of dangers. For instance, the group decided to take a short break while Senku decided to check out the river that they had been following upstream to ensure that they were on the right track.

Kneeling onto the ground next to him, Chrome peered into the water and noted with a curious gaze. "There isn't a single fish in this river."

"I know. Nothing but emerald green liverwort." The green-haired teen nodded his head before rising to his feet. "This is it for sure. Our goal is upstream from here."

"So the greatest hurdle is up ahead..." Kohaku trailed off as she turned her head towards the direction of upstream.

The corners of your lips were curled into a concerned frown as you added, "If this is the case, we should be on alert at all times in the case that thing doesn't go to plan."

"It's okay."

The sudden sound of Ginro's frightful voice filling the air caused all heads to turn in his direction where all of you were greeted with the sight of the trembling blonde taking small, shaky steps as he held the spear in front of him; never taking his eyes off the silver head.

"It's okay. It's okay. It's not black yet. It's okay. It's okay. It's okay. It's ok—" The blonde kept chanting to himself when suddenly, he was cut off by Senku jumping in front of him.

"What the hell is the sensor doing walking at the back, Ginro?!" The green-haired scientist barked in the other teen's face.

The poor blonde, who was frightened to his core, could only cry in response. "Well, you said I was going to die! I'm scared!"

Kohaku fixed her fellow village an unimpressive stare, her arms folded as she asked, "Want to switch places with me, then? Hand over the silver spear."

"Never!" Ginro was quick to respond, his eyes narrowing at the blonde as he held his precious spear away from her and declared with determination. "I'll do it! I'll do it, all right?!"

With that, Ginro the bodyguard resumed his duty and led the group safely towards the end goal.

"I-I-I-It's okay...It's okay...It's okay...It's—" The teen kept mumbling with each step when suddenly, he stopped in his track and green eyes widened tenfold at the sight that greeted him. "Chrome, Senku, Kohaku-chin, (Name)-chan..."

Chrome came to a stop next to the blonde, his eyes widening too at the sight before him. "We're here, Senku."

Said scientist was the last to arrive as he struggled to climb over the small ledge, having no energy left in his body from all the walking. Seeing your poor friend, you hurried over to assist him by grabbing onto his wrists and using your entire body to pull him up.

"I knew it." Senku panted as he tried to catch his breath, but despite that, he was grinning as he had been right all along. "We've found the source of the materials that were our greatest hurdle."

"I don't even know what we're here to gather, but I can at least appreciate that this is our goal," Kohaku commented, blue eyes glimmering with awe – unable to tear her gaze away from the scene in front of her. "It's so divine and beautiful...An entire spring of emerald green."

Right in front of the group was a beautiful, deep blue lake sitting in a crater in the middle of the mountain. Both Chrome and Ginro were also filled with the same feeling of wonder as the other teen at the picturesque view, but the same couldn't be said for you.

Now that you were standing here and recognizing what the lake actually was, you finally understood why Senku had wanted to come here and why this mission was perilous.

Everyone got to unpacking their stuff and readying the items needed to collect the last ingredient for the all-cure drug. However, unbeknownst to any of you, Ginro was walking towards the lake with a dreamy look on his face as though he was bewitched by something or someone.

Chrome was unpacking his bag when he noticed the troubled looks on both your and Senku's faces and couldn't help but asked out of curiosity. "What's up, Senku, (Name)? Is this not our goal?"

"No, it is," Senku affirmed. "This is perfect. It's this green water that we're here to collect. But the geography bugs me."

Letting out a small hum, you mumbled. "Oh, so it's the geography that is off."

Surprised by what you just said, Senku turned to you with raised brows and asked, "You can tell that there's something wrong with this place?"

An embarrassed flush appeared on your cheeks as you rubbed the back of your neck and let out a sheepish smile. "I may not be as smart as you when it comes to science, but I recognize what this lake is based on its colour since we learn about it back in high school. Furthermore, I felt that something is weird about this place, but I just can't quite place a finger on it. That's all."

"Not bad, assistant. Ten billion points for noticing that something is off." Senku whistled, causing the pink on your cheeks to deepen at his praise.

Meanwhile, both Kohaku and Chrome were watching both your exchanges with a confused expression and seeing that, the green-haired scientist began to explain. "The poison gases that form here, hydrogen sulfide and sulfur dioxide, are heavier than air. They settle in dips like this one."

Upon hearing that, the brunette started to sweatdrop as he turned to Senku with a nervous smile and asked, "Is that what the silver spear's supposed to warn us about?"

"Yeah," Senku replied. "Silver reacts with hydrogen sulfide and turns black instantly..."

That was when, from the corners of your eyes, you noticed that Ginro was at the bottom ledge that the rest of you were standing on and edging closer towards the lake with every step.

"Since when did Ginro get there?!" You exclaimed, shocked at how none of you had noticed that the blonde was missing the entire time.

Suddenly, the tip of the silver spear started to turn black and Senku was the first to notice, red eyes widening with panic as he yelled at the top of his lungs, "Get back, Ginro!"

However, his words fell upon deaf ears as Ginro kept edging towards the lake and if it weren't for Kohaku's quick reflexes, it would have been the end for him. Without a moment to waste, the blonde dashed forward and with an outstretched arm, she grabbed the other teen by the back of his shirt and pulled both of them back to a safe distance.

It was at this moment that three black crows took flight and flew towards the lake, however they didn't get far before the poisoned air killed them in a matter of seconds and they fell into the lake.

Everyone was filled with horror at the sight that all of you had just witnessed when suddenly, Ginro let out a sharp cry of fear and startling the group with his outburst.

"Go away!" The blonde kept screaming and waving his arms in the air like a madman as though he was trying to erase something that only he could see while Kohaku tried to calm him down.

"Calm down! There's no one there! There's no one there, Ginro!"

Meanwhile, you couldn't tear your eyes away from the scene in front of you and watched with wide, horrified eyes as the dead birds sank into the lake. "It melted. The bird's wing..."

You weren't the only one still reeling with shock from what just happened as Chrome turned to Senku and demanded, "What's the deal with this spring's water, Senku?!"

Said teen started to explain, "It was discovered around the 8th century, in the midst of alchemy research. In our time, it was a chemical that served as the foundation for all kinds of chemical industries..."

"Sulfuric acid," You finished in a solemn tone, driving home the severity of this chemical.

Senku heaved a frustrated sigh as he stared at the beautiful yet deadly lake with a small frown before turning to address the rest. "After what happened today, it's best that we head back to the village and rethink our cause of actions before doing any further attempts."

No one dared to disagree after witnessing what just happened and so, with that, all of you packed up and headed back to camp.

***

"And we can't make the cure-all drug for Ruri without this sulfuric acid stuff?" Chrome questioned with furrowed brows.

The corners of the scientist's lips were curled into a grimace as he replied, "Nope. We need to secure a source of sulfuric acid anyway, or chemistry won't develop any further."

Having already made it this far, Kohaku refused to give up when they were so close to saving her sister. "We'll have to push our way through to gather some. I'll risk my life as many times as it takes to save Ruri-nee. With my speed..."

Hearing that, the corners of your lips curled into a small frown as you tried to knock some sense into the blonde before she dashed off to try and be the hero. "Even if you are fast enough, it's just way too dangerous to risk your life as your chances of survival is slim to none."

"But—" Kohaku tried to protest but was interrupted by Senku who placed a firm hand on her shoulder, causing the teen to glance over at him with a puzzled look.

The green-haired scientist wasn't looking the blonde in the eyes as he spoke up, being serious for once. "Back in our age, there was a group that went to do research around an area of sulfuric acid like this one. The man in the front knelt for a moment, maybe to tie his shoelaces. He was dead."

Everyone fell silent at those three words, no one dared to make a single sound as they held their breath while Senku went on. "There was hydrogen sulfide at his head's height when he knelt. This is an accident that actually happened. Humans don't stand a chance when Mother Nature wants us dead. (Name)'s right. It doesn't matter how stupidly fast you are, Kohaku."

However, said blonde refused to believe that this was the end, not especially when she was one step away from seeing Ruri alive and well again. "Then what are we supposed to do, Senku? I have to save Ruri-nee, no matter what!"

There was a moment of silence before his trademark smirk appeared on his lips and Senku let out a chuckle. "What else? We're going to make gas masks."

(E/C) eyes widened upon hearing that and you turned to your green-haired friend, exclaiming in disbelief. "Gas masks?! For real?"

Grinning, Senku declared, "What other choice do we have? The only way to fight a chemical enemy is with chemistry."

Time skipped

With that, all of you got to work and under Senku's guidance as well as Kaseki's skillful hands, the gas masks were completed within a few hours.

Holding up the mask to the air, the scientist let out a wry chuckle. "We'll have to see how much poison we can breathe through this. We can't rely on trial and error this time. An error would mean our death."

"I'm sure it'll work, Senku." You piped up from next to him, causing said teen to snap out of his musings as he turned to glance down at you. "I'm ten billion percent that it'll work because this mask is designed by you and not once, have any of your creation or invention fail in this stone world."

After hearing that and seeing the brilliant smile sent his way, the worry in his heart faded and his face softened into a fond expression as he raised a hand and cupped the side of your face, his thumb stroking your cheek in a gentle motion – his lips curling into a small smile.

"Thank you for always having faith in me, (Name)."

For a second, you froze at the unexpected action (even though this wasn't the first since you woke in the stone world that the scientist has shown his signs of affection) before relaxing as you turned your head slightly and nuzzled your face into the warm palm, a lovely shade of pink blooming on your cheeks.

"There's no need for thanks. It's just my job as your lab assistant."

At that moment, Senku felt a small "thud" in his chest when you gazed up at with those big, round (e/c) eyes that always reminded him of the galaxy with its many wonders and mysteries where he found himself wanting to map out each and every star in there.

At this point, he couldn't deny the emotion that was stirring in his heart whenever he shared tender moments like this with you. With his intelligence, it didn't take long for him to figure it out but accepting it was another thing. After all, he has always been a man of logic and reason who believed that emotions have no place in the world of science.

However, with every passing moment spent with you, that belief was starting to falter and Senku realizing that emotions played just as an important role as logics in science. You were living proof of that fact. Although, he wasn't ready to just take thing as it was and believed he needed to collect more data before proceeding any further.

Amid his inner musing, the green-haired teen didn't realize that he had gone silent all of a sudden and as seconds passed, you couldn't help but worry, thinking that something was wrong.

Your smile from before dropped into a concerned frown as you asked, "Senku, is everything okay?"

Said teen blinked himself out of his stupor and glanced down at you, the corners of his lips quirking into a fond smile when he saw the deep furrow between your brows. Chuckling, he raised a hand to ruffle the top of your head reassuringly. "I'm fine. Just thinking of something. Nothing to worry about."

"All right, my mask's next."

Just then, Chrome spoke up and the moment between both of you broke as both your heads turned towards the brunette and noticed that he was studying the drawing plan of the gas mask.

Hearing that, (e/c) eyes lit up and you piped up, "Oh! Don't forget about mine too!"

The other teen glanced up from the paper and turned his gaze towards you, a big grin breaking out on his face as he exclaimed, "Of course, (Name)! We need all the help that we can get."

You nodded your head in agreement, unable to fight the infectious smile on your face at your brown-haired friend's