An era in which astronomical phenomena and mechanical techniques were extremely developed. There is a secret legend in the world: the Time Mark Sect, which is proficient in the "Time Technique", can use special techniques to leave invisible "Time Marks" on objects or spaces. These notches can be "triggered" at specific, precisely calculated moments, causing slight distortions in physics or space and time, thereby enabling "accurate, unbiased" crimes, just like accurately carving murder marks on the timeline.
