Metsubou Kokka no Yarinaoshi - Kyou kara Hajimaru Gunshi Seikatsu

Rudek was a nation that possessed immense wealth and the strongest military power, yet it was destroyed. Roa, a young man who had been a civil official in that country, miraculously survived but was burdened by guilt for abandoning his friends and being the only one to live, carrying that weight as the years passed.

However, one day he wakes up to find himself two years before his homeland's destruction! To prevent his nation's demise and protect his comrades, the civil official transforms into a military strategist, using his memories and the experience he gained in the future as his weapons, as he confronts the fate of destruction!