It's from the same author but instead of soldiers it was about ninjas who are partners, and the seme was ordered to kill his previous master but the uke volunteered to do it instead
http://www.mangago.me/read-manga/ai_no_konseki_yajuu_gunsou_to_aigan_guni/Second story
It's from the same author but instead of soldiers it was about ninjas who are partners, and the seme was ordered to kill his previous master but the uke volunteered to do it instead