Unfortunately you can’t see it well in the picture (reflections etc.) but all the windows of this bus are screens playing “Believe x Believe” (or in Japanese, “Biri Biri”) by Bullettrain, the theme song of “Yu-Gi-Oh! ARC-V” anime. And yes, it is mobile advertisement.
(For a bigger version of this picture both in color and black and white, check my "Japan Arekore" set on Flickr)