Sea of Quanta

The Sea of Quanta is the Imaginary Tree's mortal enemy, and an enemy to all known living things. Its progeny are the Quantum Type Beasts.

Overview
To explain in simpler terms, assume the universe is a glass of water on a table surrounded by an infinite number of other glasses of water. Overflowing water will flow along the glass walls to form a puddle in the middle of the table. The puddle does not belong to any one glass, but the water in the puddle may be from any glass. This 'puddle' between universes was discovered by scientists of the Previous Era, and named the Sea of Quanta.

The Sea of Quanta also seems to emit a 'negative influence'. This influence affects people differently; Einstein appeared mostly unbothered despite being in close proximity to a portal to the Sea, however Theresa Apocalypse felt exceedingly uncomfortable and unwell in the same place.

Scientists from the Previous Era were capable of creating a portal to access the Sea, and housed it in The Deep.