Gate
GATE 自衛隊 彼の地にて、斯く戦えり (original)
A gate to another world appears in the middle of Tokyo’s Ginza District, and the citizens of Tokyo are attacked by cavalry, dragons, and demons. Itami, an otaku who was in the area to purchase his long-awaited doujinshi, becomes the accidental hero of the day and gets promoted to second lieutenant of the Self-Defense Force. Not long after, he’s sent on a mission through the gate into the other world with typical otaku-like expectations of what he’ll find there.
Starring Junichi Suwabe, Nao Toyama
Watch "Gate" on Amazon released in 2015. It's a animation and drama show, and has a rating of 7.5 out of 10 from Imdb which is usually fine for this kind of show.