The thing that exemplifies Blue Archive the most for me are always these casual images where the girls are doing slice of life things, but the guns are always present in the image like its a casual thing. No matter how casual the girls are they are never without their gun, the gun is an indistinguishable part of their life, it blends right in with their normal activities so you'd never even notice it, but that's what makes it blue archive. The blending of war and slice of life, "life is war" or "youth is war" something like that.

>Grenades in the vending machine
>Bullets casually thrown into your shopping cart with your instant ramen
>Guns lining the wall on Sora's shop in the background
Its the casual air about it