Nice story.
As a lot is about the MC going fast up in military ranks, the story and english translation might cause some confusion there.
South Koreans are in reality conscripted for 2 years. They then usually go up from no insignia to 4 stripes (Rank: Byeongjang) over time. Which by international standards is considered E-5 = Sergeant. But a Sergeant is regularly, like in the US army, a non commissioned officer (NCO), which a Byeongjang is not.
Better US equivalent would be a Specialist E-5 without command authority, which no longer exists in the US army after reforms.
First NCO in south korea is of Hasa rank. To cause further confusion the Hasa has an ensignia of one chevron, while an US Sergeant has already three chevrons.
And if awakeners and five years of conscription were real, we would really need something like E-9 Specialist/common soldier for long time and/or strong Enlisted with no command qualification.
But these ranks do not exist in the story.