From Kodansha:
Anno Domini 1620. Europe is riven with the conflagrations that will grow into the Thirty Years War. Catholic and Protestant forces clash across battlefields ruled by sword and gunpowder alike, and mercenaries of every stripe ply their trade.
Among them is Issak, a lone Japanese warrior bearing a matchlock of strange design and fighting in service to his sworn mission to find and kill the man who murdered his master and fled Japan for the other side of the world.