During the 17th century, Europe is being devastated by the Thirty Years' War. Although the Netherlands send reinforcements to The Holy Roman Empire, almost all of them end up deserting, with the exception of a single Japanese man.

Travelling all the way from East Asia, Issak is searching for the man who murdered his master and stole something precious to him. Suspecting the killer has joined one of the opposing armies, Issak participates in the war as a mercenary, hoping to find and end his nemesis once and for all.

Issak has been published digitally in English by Kodansha USA since August 15, 2023, and in print as 2-in-1 omnibus volumes since June 10, 2025.