Japanese Naval Signal Flag #0—Code "Rei" 最初の0の日本の海軍艦隊信号-名前「れい」

The Japanese Maritime Zero Flag uses the colours blue and white.  It has the pattern of the Zulu flag but in the hoist and fly triangles is blue, while on the chief and compartment triangles it is white.

The Japanese Auxiliary Zero Flag make intuitive sense, more so than the International Maritime Flag.  Firstly, the empty hourglass shape indicates that time is up—it has reached the zero hour.  You can imagine that the blue triangles on the hoist and fly are ocean or sky.  Likewise Zero Flag follows the shape-pattern of the Zulu flag.  Thus Zero and Zulu combine for a unique flag.

 You can see the Zulu and Zero flag with Lima in the first upper left hand column.  On the right page you can see the codes that all begin with Rei.