The Self-Defense Force Goes to Another World (自衛隊、異世界へ行く Jiei-tai, Isekai e Iku) is episode 1 of the Gate - Thus the JSDF Fought There! anime.
A mysterious gate suddenly appears in Ginza, Tokyo where fantasy creatures led by men in Roman armor come out from it and attack the people. Yōji Itami, a JSDF reservist, who was attending a nearby doujin convention, takes action by organizing the police to evacuate the civilians into a palace to protect them before the JSDF arrives to stop the invaders. Due to his actions, Itami is promoted to First Lieutenant and celebrated as a national hero. The appearance of the Gate and massacre of Japanese civilians, dubbed the Ginza Incident, prompts the Incumbent Prime Minister to takes action by proclaiming Japan will send a JSDF task force backed by the US to the "Special Region", the world beyond the Gate, to not only explore the new world but also capture and demand reparations from those responsible for the attack. After 3 months of preparation, the new Prime Minister sends off the JSDF task force to their mission to the Special Region with Itami as part of the task force. After finally arriving, the task force encounter an army waiting for them and prepares for battle.
- In the manga, the invading force made a civilian corpse pile whereas in the anime, they simply were killed.
- The time after the Ginza Incident is more fleshed out with Itami, including the introduction of Kurata.
- The attack helicopters used in the anime are Cobra AH-1S, not AH-64 Apache attack helicopters as depicted in the manga.
- The first battle of Alnus Hill is depicted more detailed in the manga.
- In the manga, the JSDF attacks the Imperial force stationed in Alnus Hill one day after the Battle of Ginza rather than 3 months in the anime.