1. **Key Awakening:** When you are eight years old or above, your soul resonates and is the only key to awakening. It has different shapes (crystals, runes, artifacts, creatures, etc.) And determines the different world you lead to.
2. **World level:** Different worlds are divided into levels (E-S levels) according to the level of power contained, the strength of rules, and the height of civilization. Such as: Norse mythology (A level), Marvel universe (S level), DC universe (S level), Kamen Rider universe (B level/huge potential), Saint Seiya universe (A level), Cthulhu universe (S level/high risk), martial arts world (C level), wasteland world (D level), etc. Level represents the "upper limit" and "danger" of gaining power, and is not absolute.
3. **Ability Acquisition:** The key opens a one-time, short-lived journey to another world (the flow of time is variable). Individuals experience, contact, learn or integrate in this world and acquire unique abilities/items/knowledge. Ability strength, form, and potential are strongly related to individual qualifications, experience, key characteristics, and world rules. After being obtained, the key "cools" and becomes a status symbol and a source of power.
4. **Unique:** Even if you lead to the same world (such as multiple Nordic myths), the abilities you obtain will never be the same due to different time points, locations, and encounters.
5. **Differences in power systems:** The power rules of different worlds conflict or complement each other (such as divine power vs. Technology vs. Biological energy vs. Microcosm). Integration is both a problem and an opportunity.
