In the sequel of Isekai wa Smartphone to Tomo ni, Touya Mochizuki settles into his new world, juggling quests and spending time with his fiancées: Yumina Urnea Belfast, Yae Kokonoe, and twin sisters Linse and Elze Shileska. Amidst this peaceful routine, Touya realizes the weight of his commitments. When the elder fairy Lean seeks his help in finding the missing pieces of Babylon, a floating island created millennia ago, Touya embarks on this mission. Yet, as he unravels the teleportation circles leading to these islands, menacing monsters surface, posing a threat to the world. To safeguard his newfound existence, Touya must harness ancient technologies against these formidable foes, all while navigating the complexities of his numerous relationships.