Darkness of the Soul (心の闇 Kokoro no Yami) is the second episode of Phi Brain: Kami no Puzzle Season Two and the twenty-seventh episode of the anime series overall.
Tamaki, who was given a strange earring by one of the Orpheus Order's members, Pinochle, challenges Kaito to a Judgment Puzzle in which he must navigate an ever-changing maze inside the Root Academy Tower. Nonoha deduces that Tamaki's change in personality is the result of her earring, which possesses the same properties as the Orpheus bangle. Tamaki uses the power of the earring to increase her brainpower, but Kaito manages to successfully solve the puzzle. As Kaito reaches Tamaki, her earring breaks, returning her to her senses. Kaito begins questioning the Orpheus Order on their motives and before they escape, Freecell states that it might take a lot more for Kaito to "remember".