Senku was getting fed up with Chrome. The man, his fireman, was supposed to be shoveling coal into the steam engine firebox, minding the pressure levels, keeping an eye out for safety concerns, but instead was incredibly distracted, going slowly, staring outside (not towards the front, where his eyeballs would be useful), even dropping coal straight onto the floor. Senku quickly gathered that coal up and chucked it into the firebox so it wouldn't ignite inside the cab (he'd been a fireman himself for years before becoming an engineer), then turned on Chrome with a glare. "Whatever suicide you're planning, I don't want a part of it. Wake up!"
Chrome was appropriately apologetic, stammering excuses. Senku didn't hear his reasons, though, frustrated with Chrome and even more frustrated with his larger situation—his proposed steam engine design had been turned down, again, before he could even pitch it. And he'd been warned that his job was in danger if he kept experimenting.
His brain was occupied with that as they eventually pulled into their next stop (a small-town platform with literally just the platform and a sign off to the side), and so he was completely unprepared when Chrome leapt out of the engine car and ran into the arms of a blonde woman on the platform instead of doing his job.
"The hell are you doing?" Senku shouted out the window after taking a moment to process that, yes, Chrome had left the train (and taken his bag of possessions with him). Not filling the tender, not checking that parts were oiled and maintained. Not telling Senku what the hell was going on.
Chrome looked at Senku, then at the woman, then at Senku again. "Sorry, Senku," he called, sounding very firm and dramatic, "but I have something I need to do." And walked away, the woman holding onto his arm and looking up at him lovingly.
"Get back here!" Senku shouted, but the man didn't turn. "Chrome, how the hell will I operate this train?!" He'd be late for every stop if he had to do both his and Chrome's jobs! And then he'd get fired anyways!
With a shout of frustration, Senku hopped out of the engine to check on the coal and water levels—because Chrome sure as hell hadn't been giving updates. And then he'd need to do a maintenance check, and update the conductor that one of the critical members of the steam engine team had just bailed with his girlfriend, and figure out how the hell he was supposed to keep the train moving while keeping an eye on the tracks, and—
"Um," said a high-pitched voice, and Senku looked down from the tender to see a skinny blond teen looking up at him.
"The hell do you want, kid?" he snapped.
The teen scowled at him, pulling back a little. "I was going to ask for a job, but you seem rather rude."
Senku pinched the bridge of his nose. It wasn't this kid's fault nothing in his life was going right, and it wasn't fair to take it out on him. "Don't take it personal. My fireman just ditched me." He sighed, then eyed the somewhat skinny youth. "You any strong?"
"Yes," he answered firmly.
"Hm. Let's see about that." He got down (water levels were acceptable, coal was fine) and waved the kid over to the engine. "Just to the next stop. I'll pay, so show me what you got."
The kid beamed and scrambled up, practically vibrating in excitement.
To Senku's absolute surprise, the kid was strong, fast, and very quick on the uptake. The train reached the next stop within a reasonable margin of error, despite the change in personnel. "What's your name, kid?"
"Kohaku. What's yours?"
"Senku." He straightened his hat. "You're not a complete moron, so do you want a job?"
Kohaku narrowed his eyes, then snorted. "Yes, alright. Even if you are the rudest man I've ever met."
Senku smirked widely. "You'll meet worse, in this line of work. Now go get yourself an apple or something. Back in ten."
Kohaku just laughed and hopped down to the platform to go buy fruit from the little market there (good to take breaks when learning, to give you a chance to absorb information—or so his dad's philosophy went).
As he checked the water in the tender again, Senku wondered what this kid was running from—why else would he accept such a job, and so quickly? But he didn't spend long with the thought. Kohaku was a strong, hard worker, despite having uncalloused hands and a frankly annoyingly positive attitude, and Senku needed someone strong to help him run the train so he could continue his experiments improving the engine design. (Of course he wouldn't stop—those old windbags would never see another invention of his, never even get a hint of his experiments, and maybe he'd start his own company, show the world what he could do.)
He shook his head thinking of Chrome again. Running off with some woman…who'd looked a bit like Kohaku, actually…
Hm. A mystery. Was it one he cared to solve?
…nah. He had things to do.
Like get this train back in motion. "Kid!" he shouted as he climbed down, "let's—"
And Kohaku was there before he could finish, fast as could be. Shorter than Senku, with big blue eyes and a spiky halo of hair reminiscent of a lion's mane. The kid grinned at him, head tilted. "Are we leaving now?"
He spoke formally. This kid was educated. Why'd a fancy little lion cub take a job as a fireman?
…not that he cared. "Yeah. Get your ass back in the cab. I'll show you the rest of what you gotta do."
Kohaku giggled—giggled, like a schoolgirl—and hopped up with ease.
Maybe, if Kohaku was a quick enough learner, he could have the kid do some of the engineer's tasks so he could focus on his experiments. With a manic grin, Senku climbed up into the cab. Now that was something to get excited about!