Kerberos Saga Rainy Dogs is set in the Kerberos Saga's alternate timeline, where Nazi Germany won World War II, eventually denazified and restored the Weimar Republic, and occupied Japan (part of the Allies in this timeline) to establish authoritarian rule; however, their attempts at establishing a new government led to increased poverty and class stratification, resulting in the rise of anti-government movements and terrorism, most predominantly the Sect.

[1] In the restaurant "Papa's Lunch Room" in Havana, Cuba, multiple people—a yakuza in a tuxedo, a middle-aged bearded man in a cassock, an old smartly-dressed violinist, and hitman Golgo 13—wait silently at separate tables.

The waitress, who survived the shootout, unbinds the chef and heads to a hotel in the outskirts of the city, where she alerts the occupant of room 203: Koichi Todome himself.

The plot of Kerberos Saga Rainy Dogs happens before the events depicted in StrayDog, Koichi left Latin America with his suitcase and is now living in Taiwan.

Kerberos Saga Rainy Dogs was first published in Ace Tokunoh (エース特濃, Esu Tokunou), a comic magazine owned by Kadokawa Shoten.

The previously unreleased prologue "Act 00: Set Up" was added to help in the understanding of the complex background and the 2003 short story "The Killers" (first issued in Ace Tokunoh vol.1) was also included as an epilogue.