Fate/Grand Order: Zettai Majuu Sensen Babylonia

Shonen anime with large scale battles. Humans fighting against large monsters. Warriors protect a city surrounded by a large wall from monsters. Both set in the past (fictional version). 

both anime use past heroes as characters in their anime, but instead of using hero spirits, Touken Ranbu uses the character's weapons as characters. and both anime tell the same story to protect history that is in trouble 

Watch this one is super intense and so many twists and turns, and worth watching after first order. 

Though the plot and structure of each show is completely different from the other, both succeed is conveying one specific point: scale. The enemies are gigantic monsters that are constantly putting the world and the lives of the characters in danger, and victory is never achieved easily, usually happening at the last minute after the characters have exhausted all of their resources. 

Both are adaptations of the gacha-game with separate plot from original based on universe, where main events are only mentioned.  

-Both are similar era -Both involve magic and supernatural  

Masters who command "servants" must protect the universe from external/unavoidable doom. There are different classes and specialties-- a different history and a different path for the MC. Who would have thought "the weakest link" is carrying the weight of a world on their shoulders? Build a harem, or don't... it's the life of a hero. Neither shows are too original or especially unique, but it's filled with comedy and tsunderes.