Ochiru Iro wa, Kohakushoku

In a world still engulfed in war, Theo, who serves as a military lieutenant, feels uncomfortable around Kaguma, the captain of another unit, who constantly hits on him. However one day, while shielding Theo from a sniper, Kaguma sustains an arm injury that takes a month to heal. Feeling responsible, Theo offers to nurse Kaguma for the month until he recovers, but when he witnesses Kaguma masturbating, Theo ends up helping him deal with "that" as well...?

(Source: Cosmic Publishing, translated)

Note: Includes one extra chapter.