The Sacred Army HQ (神聖政府軍本部, seishin seifugun honbu?, lit. "Sacred Army Headquarters") is the base of operations for the Sacred Army, the rebel army that opposes the Grand Bell. It's located in Historical City Enna. Although the place is relatively small in comparison to the Grand Bell Hall, which also reflects the difference in size between their military forces, it still shows splendor and magnificence due to being a rebuilt part of the Enna Palace, which was razed in an IPD Outbreak several years ago.
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Although the game itself considers this area as a dungeon, it doesn't have anything notable: there are no enemies, event battles, bosses, treasure chests, Talk Topics, Synchro Topics or IPDs to be found here. It has to be mentioned, however, that this area is exclusive to Luca's Route: in Cloche's Route, this area is never added to the Town Map, and therefore, it's rendered inaccessible.