- Twin Laws: The Spirit Realm Continent is woven from the Laws of Nature and the Laws of Machinery. Plant and animal spirits depend on the power of nature, while the mechanical cores left behind by an ancient civilization are eroding the ecological balance.
- The Secret of Her Scent: The protagonist's innate Spirit-Soul Fragrance is the mark of an ancient pact. Each wisp of fragrance corresponds to an elemental ability, and is also a key to opening the forbidden gates.
- The Temporal Conspiracy: The immortal realm contains a Corridor of Time, where key figures repeatedly face fateful choices at different points in time, forming a closed-loop mystery.
