Mayu Otsuka works at the 4th Foreign Affairs Department in the Japanese National Police Agency as a liaison officer with the National Astronomical Observatory of Japan. She wrote a story about a masked man that supposedly seemed to be a dream, but she isn't sure. Hei and his comrades got themselves a new task and are looking for a numeric password with a sample. A contractor took it from the Gate and buried it under a blossom tree. As events unfold, Mayu seems to fall in love with Hei, while Saitou struggles to confess his feelings for Kirihara.

Suo and July find themselves in a dangerous situation thanks to a double-crossing supposed ally. Later, when the young pair is abducted by an especially sinister Contractor, BK-201 must spring into action.