Gun Frontier

Gun Frontier is a historical manga series by Leiji Matsumoto in Play Comic from 1972-1975. In contrast to some of his other series which took place in space, this series is placed in the American West during Earth's American frontier period. It introduces the first uses of Tochiro and Harlock in the Star System before they're more iconic role in Space Captain Harlock. A few decades later, a novel sequel written by Matsumoto titled Gun Frontier II in 1999 and an anime adaptation in 2002.

Plot
In the large west Gun Frontier, the duo of Tochiro and Harlock travel the land looking for a place to settle down while traveling with the mysterious beauty Sinunora. Tochiro is a Japanese drifter who was washed up in the West and is looking for other Japanese immigrants who were chased out of their village. Sinunora's true purpose for going with them was to find the Japanese settlers in question and destroy them. But her stay with Tochiro made her change tactics as they grew close, admiring Tochiro's struggle.

Relationship with other series
While taking place in different time periods that are separated by centuries, the main characters Tochiro and Frankling Harlock, Jr. are implied to be related to Tochiro Oyama and Captain Harlock as told by a few interviews.