Cars decorated with anime artwork, itasha, may be old hat, but an air of novelty still surrounds the rare ita-bus, perhaps due to the sheer amount of photoshopped buses floating around (see below for some interesting examples, especially the Shinku Liner), outnumbering the confirmed instances by far.
However, here we have a very definitely confirmed example, and it happens to be advertising a bishoujo game and mixed media franchise, 絶対衝激～プラトニックハート～ / Zettai Shougeki – Platonic Heart. Whether we can call it an actual eroge remains to be seen, although it is certainly not lacking in pretty ladies in CG form.
In fact the bus has video monitors installed, so it is more of a mobile hoarding than a public transport vehicle:
Shinku Liner? Some probably shopped buses for reference: