The Forbidden Fruit (禁断の果実 Kindan no Kajitsu) is the thirteenth episode of Phi Brain: Kami no Puzzle Season Two and the thirty-eighth episode of the anime series overall.
Souji sets up a sliding puzzle for Kaito, also threatening to blow up the academy should he fail. As Cubic, defiant that Souji hasn't changed, goes to search for said bomb to prove his theory, Nonoha and Ana end up helping Tamaki with her paperwork in order to get her to evacuate. As the game progresses, Souji soon feels the advantage of the replica ring and starts to enjoy it. However, Kaito soon expresses his joy at such a fun puzzle and turns it around for the win, which leads to the replica ring being destroyed. Afterwards, Souji explains what he had learnt from wearing the ring, deducing the rings will destroy themselves if their user feels they have lost. The next day, Tamaki is voted student council president whilst Souji goes on a journey, leaving Kaito with another truth he discovered about the rings; their desire to join with him and become true Orpheus Bangles.