Blue Sun, Red Moon (蒼い太陽、緋い月 Aoi Taiyō, Akai Tsuki) is the fifteenth episode of Phi Brain: Kami no Puzzle Season One and the fifteenth episode of the anime series overall.
Kaito becomes angry when he notices Rook to have done something to Cubic. He and Nonoha go to one of Rook's old living quarters, where they learn of Rook's disturbing childhood. After hearing from Nonoha about some ruins where Kaito and Rook used to hang out, Ana goes to investigate and encounters a POG Giver, who presents a maze-type Kenja Puzzle, which Ana solves easily. However, things get hectic when Gammon and Cubic attempt to rescue him, but Ana makes it out okay, retrieving a wooden puzzle Rook made for Kaito, the sight of which also surprises Rook himself.