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.
The Black Abyss begins based on what they have told the MC and ML about. They originally had no plans to create the organization but began it later to protect ability-holders who weren't connected to the government. They are overall good guys who protect their members, minimize damage to their surroundings, and avoiding killing or stealing other people. As far as we know, they've never even killed a human. In the books, they were this fearsome organization that fills everyone with dread, so the government, who knows the truth, will even threaten to send their prisoners to the Black Abyss for interrogation... Not knowing anything, those people spill the beans because they're terrified of the book's version of the Black Abyss. The leaders of the Black Abyss are good guys who generally protect the weak and only fight those who attack them first. Don't attack them, and they're pretty nice.
Instead of being enemies with the Chinese government, they actually work together and rely on each other quite a bit.
The book's protagonist has nothing but a gang of transmigrators around him trying to gain his favor and control him. Although a couple of people try to do that with the MC and ML, they're generally too chicken to try taking advantage of the "villains."
The monsters of the other world show up ahead of schedule and confuse all of the transmigrators' timelines.
At this point in the story, she is even falling for that ML trash.
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.
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.