Immediately after being introduced to the main cast, I thought of Anohana: 5 childhood friends, seemingly inseparable, that were torn apart by a traumatic event, only to reunite many years later fighting for the same goal. This is certainly the case for Daisuke and his friends Keisuke, Marimari, Gai, and Gai's sister Lu. They rebuild their friendship much like the cast in Anohana.
A sudden massive event causes a change that brings out the main character's drive to protect everyone and be the hero.
Humans fighting against larger creatures with the aid of combat weapons unlike what currently exist.