Armin x Aqua (Attack on Titan and Konosuba crossover)

two Different Worlds Collide into one. what are the events of these worlds and why do they collide together. a blonde haired boy named Armin found his world looking completely different from how he remembered it. the grass seem to be greener and for right now there wasn't giant Titans running around. just a field of nice cherry blossom trees with an interesting blue-headed girl sitting under them. it was almost like something written in one of the books he's read. it felt like it was a fiction story. then the girl would notice something a giant colossal human in the distance running around kicking the trees from the ground. as much as the Titans terrified arm and he jumped into action to get rid of it as it clashed to the ground that's when she realized that something is changing her world too. who is this boy and what was that thing?