Decisive Battle (決戦 Kessen) is episode 17 of the Gate - Thus the JSDF Fought There! anime.
Plot
Anime-Manga Differences
In the anime, Towato and Mowto are killed much faster than in the manga.
In the manga, the Dark Elves elders are seen guiding the JSDF's armored battalion to Itami's position while in the anime, they go their all by themselves without any guidance.
In the manga, King Duran is seen accompanies the JSDF to access to his kingdom and witnesses the death of the Towato and Mowto. In the anime, King Duran doesn't accompanies the JSDF to his kingdom or witnessing the death of Towato and Mowto.
In the manga, Giselle is seen to check on the claim of others about Itami defeating the Flame Dragon while in the anime she believes the claim of Rory, Tuka, Lelei and Yao right on the spot.
In the manga, Yao argues about the awakening of the Flame Dragon and trying to attack Giselle for all the atrocities caused by the Flame Dragons to her people. In the anime, she just simply confirms whether Giselle awakes the Flame Dragon or not while letting Itami takes care of the rest.