These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Szilard Quates, the immortal Mad Scientist and alchemist. Szilard believes in knowledge being the most important commodity in the world, and to that ends devours immortals for their knowledge. After becoming immortal, Szilard devoured the brother of the immortals' leader before being driven away. Szilard creates Artificial Human homunculi to serve him, abusing them mentally and physically. He also developed his own immortal potion which he feeds to intelligent people before devouring them to amass their knowledge without working for it. He isn't above straight up murder for his purposes either. It's mentioned at one point he gains no greater joy than in devouring others.
Fermet, another of the original immortals, was the caretaker of the immortal child Czeslaw Meyer. However, once they were immortal, Fermet revealed his true colors as a vicious sadist who Would Hurt a Child by torturing Czeslaw for years and years, with new, inventive ways, ranging from throwing him into a roaring fireplace, to making him bathe in acid. The excuse was to test the limits of immortality. The truth was simply sadism. Then we find out that he's the reason why SAMPLEnote a cult whose members tortures children in the hope that the children will receive any pain directed at themselves really spread across the world. He also killed Monica, giving Huey his Start of Darkness. And to top it off, he sets things up so that Niki, a woman who loved him and who was also a close friend of Huey and Elmer, would be killednote or horribly scarred, as it turns out, and then tells Elmer and Huey that it was their bomb that did it just to see the pain on their faces. And why does he do all of this? Pure sadism. He finds it fun.
Creepy Awesome: Claire Rail Tracer Stanfield is a standout here. He's probably the best fighter and the most batshit out-of-his gourd character in the series. Now go look through the character page and consider the full implications of that statement.
Draco in Leather Pants: Fermet and Huey are baffling examples; there exist a small but loud fraction of the fanbase who perceive Fermet's abuse as his twisted way of showing "love" to Czeslaw (ignoring the fact that Czes learned a long time ago that Fermet never truly cared about him and only took enjoyment in seeing him in pain), and who insist that Huey is at least a tiny bit regretful about his treatment of his daughters, even though it's made abundantly clear that he doesn't care about either of them, would off them both in a second, and views them as nothing but experiments - that failed.
Granted, there are a lot of likeable characters in this series. Ladd, Claire, and Chick in particular are extremely popular.
Chane is one for Narita himself. Purportedly, she was originally slated to die during the events of the Grand Punk Railroad novels. However, he became fond of her, and subsequently spared her.
"Funny Aneurysm" Moment: You know how members of the Martillo family find much amusement in the fact that Firo manages to remain a virgin into his nineties (especially since he's been married for over twenty years)? In Another Junk Railroad featured a conversation between Firo and a concerned Berga that heavily implies that Firo has a Paralyzing Fear of Sexuality... because he was almost raped when he was younger.
God-Mode Sue: Surprisingly averted with Claire. The writer has stated that the reason he doesn't get his own plot line is because of how easily he could overtake the entire series.
Claire Stanfield is supposed to be a secret character. The fact that he exists is only the beginning. If you've been reading this page, it's likely you know everything about him at this point.
It's also rather telling that in the opening, while every other pivotal character is given a proper introduction, he only gets a "blink and you'll miss it" appearance.
Jerkass Woobie: Huey Laforet. While in the present, he's a complete and utter sociopath, it's revealed that he became this way after he lost everything he cared about, one by one. He even was a normal kid until his entire village was wiped out by fake inquisitorsnote actually members of SAMPLE when they all sold each other out, accusing each other of false crime so that the torture they were being subjected to would finally stop. The first one to die being his mother didn't help. Then he finally found someone he could love: his wife Monica. It was only after she was killed by Fermet that he became so cold and uncaring. He's not a good person, not by a long shot, but there is a very heartbreaking reason for all this.
Czeslaw, when not being a trauma-induced Creepy Child. His horrible past aside, his occasional homicidal tendencies in the name of self preservation as well as his less than kind disposition at times could make the argument for him being closer to the Jerkass Woobie.
Also, Niki from the light novels.
Jacuzzi, with his crippling shyness and constant tendency to burst into tears makes him one of the characters that you just want to hug tightly.