While writing Gantz, Oku took a break and made Me~teru no Kimochi, Love Laughs at Locksmiths. In one page, you can see Gantz players, in Gantz uniforms and with Gantz guns, in the background.
Since this is the Gantz Wikia, I'm only mentioning things related to Gantz. For more information, see the article on the official Wikipedia. Wikipedia:Me~teru_no_Kimochi