You might remember Keigo Shinzo from this roundtable with Taiyō Matsumoto and Inio Asano which made the rounds a few weeks back; here he draws a pair of lovers fucking maniacally while Godzilla smashes their town. Note that this is *not* dōjinshi, but the artist’s contribution to a special all-Godzilla issue of the mainstream seinen magazine Big Comic Original.
Additional digging hasn’t shown much else at the moment. I found a teeny tiny image of the full page that Godzilla: Monster Warrior panel comes from, along with the cover of the anthology it comes from via the IDW Forums.
royalboiler, this seems like something you and James Stokoe would want to know about.