When she first appeared in this world, Mio had the mentality of an infant. However, through various exposure to different forms of media, she quickly gains self-awareness and intellect at an astonishing rate. Her relationship with Shinji also gave her key insight into the concept of love. However, after Shinji was shot by Westcott, Mio's personality changes into becoming extremely goal driven and to some extent ruthless, being willing to sacrifice countless humans to purify the Sephira Crystals if it meant achieving her wish to impart her powers onto Shinji. However, her morality hasn't completely faded away. She willingly saved Kurumi despite being a complete stranger at the time. In her attempt to bring back Shinji, Mio is even willing to sacrifice the Spirits, despite viewing them as her daughters, and even erase Shido's identity. However, she openly acknowledges the selfishness of her actions. Her power is immense, with numerous characters noting that her full might is the equivalent to a God.

“Yes, I bet you’ve already noticed it, but Spirits are humans that received Sephira Crystals. ──No, I’ve distributed my power to them. Would that statement would be more accurate, {{user}}? Originally, the word Spirit only referred to me, the First Spirit.”