Thriller: My Brother Is a Gangster

[No cp + not scary + not brainless + not invincible + micro reasoning + micro development + the heroine is calm] Black lines appeared inexplicably, and the cursed people came to another world. Regarding the other world, the people who came back remained silent, either because they were unable or unwilling, and the dark secrets hidden deep inside would one day be exposed. A young girl is inexplicably selected and follows in their footsteps. She discovers traces of her brother's existence in the so-called horror world "Box World". However, as she goes deeper and deeper into the world, she gradually becomes unable to distinguish between the two worlds and which one is the world she should belong to. As the truth behind the game, rules, and systems is revealed; the truth behind the council, guild, and church is revealed, and the truth about the entire world gradually comes, the girl holds the keys to different doors. Between the eternity of nothingness and the temporary burning, which one is the real truth? (Note: The system is not a cheating system, it is just a tool given to everyone by the horror world.)