The war between Scouts and titans is over and Scouts win the war but only few members of scouts are survive while Beast Titan are succeed to run away from the battle field. Attack on titan episode 55 shows us the conflict between the scouts as Armin and Captain Erwin both are badly injured and Captain Levi want to give the injection of titan serum to Commander Erwin but Eren and Mikasa want to give that injection to Armin.
Meanwhile, Beast Titan rescue Reiner from Hange and he run away from there. Captain Levi, Mikasa and Eren are arguing to each other and give their point of view towards Armin and Cammander Erwin. This the typical situation for the scouts because both Armin and Commander Erwin are extraordinary intelligence and both play a special role to defeat titans. But somehow the senior of the scouts Hange and Captain Levi decided to give the titan serum to Cammander Erwin. Although at the moment, Commander Erwin himself refuse it and the captain Levi realizes that commander Erwin faces pain and scarification in his life and his decision mande him a demon and his life is a hell so Captain Levi decides to give the injection to Armin and left Commander Erwin to die peacefully and walk out from this hell. This season gives this role an awesome ending.