Minami-ke OVA bundled with the 10th volume of the manga.

Sendo Kazuki, failed the entrance exam for the art college he was applying to, His childhood friend, Kuhonbutsu Taishi forced Kazuki to enter the doujin (private publishing) world. (Source: AnimeNfo)

The story is about a 9-year old boy named Wataru Ikusabe that is magically transported to a magical realm of the gods called Soukaizan which he is supposed to save. In his quest to save the realm, he manages to transform a clay sculpture into a somewhat autonomous (small) Super Robot. (Source: Wikipedia)

The third series, The Last Train is set with 26 stories during a bizarre train ride that Gregory embarks upon. (Source: AniDB)