The forest is located just outside of Kazamatsuri; it is very vast though people are prohibited from going too deep into it due to it being the place where summoners and superhumans fight and kill each other. The city, as well as the forest are Gaia's territories. Gaia considers the forest as sacred ground as much of the Earth's energy flows through it; they use that energy to fuel their familiars in places called hot spots, summoners enter the forest with regularity and create tree-familiars; tree men, however as Gaia drains the energy of the forest, it becomes more and more polluted. The forest is the birth place of the Key and the main reason Gaia and Guardian fight in it. Some places in the forest are linked to a closed space called the City of Stone.
- Lucia's Route is the only route where nothing specific takes place in the forest.