From Yen Press:
Bedridden and abandoned, Takuto Ira spent his days in the hospital trying to beat the illness that was slowly killing him.
His only solace lay in the nation management strategy game Eternal Nations, where he had built a reputation as the greatest player to ever live. After succumbing to his disease, Takuto awoke within the game next to Atou, the Hero unit for his favorite civilization, Mynoghra. Now they’ll set out to conquer the world together (again), one unit, settlement, and level at a time!

Original Manga