Rumi's primary intention of joining the Regular Army is because of her ailing mother, who was suffering from weak heart, and her older sister, Madoka, who was physically weak, so that both of them can make use of the Regular Army's medical facilities for treatment. During her training, she was accidentally shipped to the frontlines after a paperwork fiasco. Despite the fact that she has not completed her training, she manages to emerge from the battles unscathed.
After the first conflict with the Rebellions, Rumi is given a chance to resign from her position and carry out the rest of her life as a civilian. But she declines the offer and transfers into the Regular Army's Intelligence Division. As a supply sergeant, she packs incredible amount of cargo in her backpack and tries to deliver them to the friendly forces out in the battlefield in hopes to help them win.
However, she is horrible at remembering directions, and wanders off to just about everywhere there is a path and often appears out of nowhere and disappears into the thin air again. Because of this, other soldiers call her "The Wandering Ghost."
Her sister, Madoka, appears to have joined the military to become more physically fit. However, it is likely that she also became thrown out into the battlefield as a result of paperwork mistake.
In Metal Slug 3D, she also proves to be a handy mechanic as she invented the garage to customize Slugs.
Personality
Rumi was a normal girl that concerned with her family's health decided to sacrifice herself. When she was sent to the battlefield, she cried but did her job pretty well.
