He lived in the modern world, but demons and magic became real one day. The only way to kill these things was to use a new concept called skills, and culture changed greatly. Even so, the world was destroyed more and more every day. When Riley was born in his previous world, he first held the holy sword at three years old. From then, he trained and trained to kill the enemy destroying the world. He did as he asked in his despair. He killed humans and demons. In exchange for saving one town, other people would die. When the people said they were better off without him, he left them alone, and they still died. No matter what he did, people blamed him. He died fighting the demon king, who treated him more respectfully than most of the humans he met.
Since the modern world turned into a post-Apocalyptic setting, the most emotional struggles he had were against humans themselves. Since everything went to Hell, crime and chaos became prominent. I believe he first kills a human when he is seven. His teacher raped his sister, so he eventually hunted down and killed his own teacher. His "best friend" actually plotted against him and murdered his parents, and he chose to chase and kill his best friend once he found out years later. The priestess he served cursed him to be unable to commit suicide. It sounds like a warped blessing until you learn that she was extremely corrupt and guilty of any number of crimes. By forcing him to live and obey her bidding, he witnessed and participated in atrocities under her command.
He truly saw the worst of humanity. As he died, his only goal was to rest in peace. When he was reborn against his will, his intention was to do anything to avoid living such a hateful life again. Like one of those reincarnated-into-a-villain series with MCs who try to avoid death flags, Riley does everything he can to avoid hero flags. He fulfilled his duties before, and he wants nothing more of it.
He becomes completely favored by the dragon king once he joins up with the dragons, too.
We also hardly know anything about how these two were in an "accident" that sent them to the past. Are they from a sci-fi future, where things like time travel and magic-like things are possible? Are they actually fantastical creatures that only recently developed the ability to fall through time? Are the two of them destined to be reborn together again and again? I hope the series answers these questions in the remaining chapters. We know hardly anything about their lives before falling back in time.
Later on, we learn that he is just very empty and has no passions of his own, which is why he was turned into a skeleton. It seems their personality flaws from before reincarnation heavily influenced the monsters they were turned into. In order to become stronger, they have to face their flaws head-on and work to change themselves. This will be great for character development as the series continues.
He began losing his hearing as he grew up and hated wearing hearing aides, so he pretended to hear and understand his classmates. When he started wearing them, he realized they had been making fun of him all this time. This turns him into an expressionless and aloof character, who usually keeps his mouth shut. His eyesight is also poor, but he manages that well with glasses.
Considering all of that and the fact that he has no combat ability, he really undervalues himself.
the mystery of how Du Ze was sent to that world in the first place. It looks like the God of Light and the Gnome God of Forging are both looking for him. Was it their doing, or did the writer actually take part? What do they want with him? Why do some of the other characters feel intimidated by the weakling Du Ze? How does the prophecy Du Ze saw play out? Did he really receive that doujinshi by accident, or did someone send it to him on purpose?
A sleezy character shows up for a while and causes some tumult in the beginning. The MC hooks up with him a few times for fun. Later on, he brings down the mafia and reappears as a serious business owner. I guess you could say they thought they were playing with a kitten, but he actually turned out to be a tiger in disguise. When his brother is imprisoned for his crimes, the MC seduces their arch-enemy in order to save his life and also get some cheap revenge on the bastard. Since he is quite skilled at business, he becomes an irreplaceable member of the staff.
One way he does this is by secretly becoming a crime lord.