The dungeon is in Korea, but as an esper with a pretty specialised power niche Haru is used to occasionally having to go international for these dungeons, and the fact that he already speaks Korean is definitely a bonus. The espers he's going to be working with are all in Quasar Guild, which is the largest one in Korea and which has just recently acquired a very powerful teleportation esper, one whose power can be stored in batteries Quasar also happened to already have in its possession, so they're covering the teleportation cost for Haru to get there.