Welcome to Japan, Ms. Elf! (MANGA) Vol 3 by Makishima Suzuki

Kazuhiro and Marie had been enjoying their lives in the dream world, but now they've been attacked by a group of bandits, and the child they're holding captive! The two of them need to save the child, Mewi, along with trying to solve the mysteries of the ruins. On top of that, Kaoruko from the library has invited them out for a chat...