Earth

Mentioned as the home of the chess champions the Workers named themselves after.

Ryoka thinks about her home world, its pop culture, and how its animals compare to the monsters here.

Referenced as the source of dangerous technological secrets, such as firearms and nuclear weapons, that Ryoka is terrified of bringing into this world.

Ryoka internally lists it as the origin she must keep a closely guarded secret.

Erin notes that she is no longer on Earth while justifying her aggressive playstyle in chess.

Erin feels like a traveler in a strange part of Earth while looking at the foreign architecture.

Erin compares the local wildlife to Earth creatures and notes her limited knowledge of Earth's languages.