This stitch incorporates the darning stitch and the holbein stitch. This stitch a kind of lovely geometric pattern that can be used as a patterned filling over large areas.

You need to know the darning stitch  and the holbein stitch to understand this tutorial.

japanese_darning_stitch_1     japanese_darning_stitch_2
Fig 1: First make rows of running stitch in a brick like manner, as you would in darning stitch. Try to keep the stitches longer and the spaces shorter for a better effect.   Fig 2: On the return journey of the stitch, join the running stitches on the upper and lower adjacent rows. These straight stitches that will join the running stitches would be slightly angled, as shown.
japanese_darning_stitch_3   Fig 3: The finished pattern would look like this.