Plain of consciousness.
'So, I'm here again? ... no matter how many times I come here, I never get used to it…'
Rio's plain of consciousness is a vast and empty place; there's nothing in it.
The plain of consciousness is something that every awakener has, and they can access it either willingly or when they are completely unconscious.
Rio fell unconscious after becoming exhausted from using too much mana.
The plain of consciousness is basically the reflection of your mentality and insides; it is a representation of the deepest parts of your soul.
Everyone's state of consciousness is very different and unique to themselves, as everyone's own life is vastly different from others.
A plain of consciousness also shows the state of mind a person has; if someone is happy, their plain of consciousness is filled with vitality and liveliness, and if the person is in pain, it's filled with their painful memories.