Rose Guns Days Season 1 Vol. 1 (manga)

After suffering unprecedented disasters in World War II, Japan accepts the American and Allied Forces' terms of unconditional surrender. Now the citizens of a ruined nation, the people of Japan come together amid an influx of influences and immigrants and--cunningly, carefully--survive...
This is the unrecognizable Japan to which the sharpshooting, sweet-talking womanizer Leo Shishigami returns three years after the war. Against this backdrop, in the spring of 1947, everything is set into motion when Leo meets Rose Haibara, the madam of Club Primavera...