Futari Bocchi Densetsu

 
Japanese Title: ふたりぼっち伝説
Year: 2004
Publisher: Shonen Gahosha
Serialized in: Young King Ours
Imprint: Young King Comics
Volumes: 1 (on hiatus?)
Translation Status: No known English translation available
Information/comments: The title means something along the lines of "A Legend For the Two of Us," which is fitting considering the series has only two recurring characters.  This is a gag manga featuring very short chapters with a Lara Croft-esque treasure hunter named Martina Springer (マルチナ・スプリンガー) and some skeleton guy who I don't think has a consistent name.  The face of the skeleton appears frequently in SS' other series and doujinshi, and Highschool of the Dead referenced the series by showing a fictional "Futari Bocchi Densetsu volume 108" on the floor of the infirmary in chapter 20.  Notably, although the series contains a large-breasted female character, it has very little in the way of "fanservice" when compared to other SS series.

I do believe this was SS' first published work, and it may even predate his earliest doujinshi.  Although the first volume was released in 2004, serialization of the series started at least as early as 2003, and may have even started in 2002.  In the back of the volume is a message of congratulations from Koshi Rikudo, whom SS once worked as an assistant for, for having his first volume published.  Unfortunately the series was apparently unsuccessful and is currently in limbo, with only a single volume available.