Below is a walkthrough of the Ancient Dragon main story event in Rune Factory 5.
Client: Livia
Location: Belpha Ruins
Objective: Retrieve the bone from the Belpha Ruins
After a giant earthquake rocks the town, Livia will task you with heading into the Belpha Ruins to locate a bone. Travel to the Belpha Ruins B3.
Belpha Ruins B3
Head into the big open room to trigger a boss fight against Cerberus. Defeat him then follow the room south to arrive at a hallway with a save point leading to the Belpha Ruins Depths. Head through the doorway.
Belpha Ruins Depths B4
Work your way through the level until you reach a circular room. When you arrive here, head down the northeastern path. Defeat the enemies there then you’ll find a pink switch. Press the switch to lower the pink gate. You’ll want to head to the northwestern path. Again, defeat the enemies there to find a blue switch. Press it to lower the blue gate. Next, travel down the southwestern path where the blue gate was to arrive in the newly accessible area. Flip the yellow switch here then travel to the southeastern corner where the yellow gate was. Defeat the enemies here to obtain the chest. After that, head to the northcentral path to head deeper into the dungeon.
Belpha Ruins Depths B5
On this floor, use the save point then head into the big room. This will trigger a dialog event that leads into a boss fight with the skull dragon. For this fight, stay behind the dragon, damaging it when you can. It’ll use a lunge attack and will occasionally summon purple and blue flames that follow you around the room. After you defeat the monster, another dialog event triggers. When it ends, head into the Silo and bring the bone to Livia to complete the event.