Hiroshi Kokusho was an ace of his high school's rugby club and used to receive attention all over the country. However, his aggressive play and selfishness got himself injured and he had no choice but to retire. Hiroshi got a job and lived alone after graduating from high school. However, a fight caused him to get fired from his job and he got kicked out from his apartment. A man then approached Hiroshi and said that he will introduce him to a perfect job which turned out to be the "Japan Ground Self-Defense Force" that protects the country's peace and security. Hiroshi, who used to be an immature man, got enlisted and became a full-fledged self-defense officer while wearing the combat helmet.