The broken seal

Start this quest talking to Yin Tugao in Bloody Plain.
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Go the 3rd Floor of the Cave of the Conqueror and talk to a Demon and to Broken Soul Demon.
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Now you must go to the 4th Floor to meet Monstrous Soul Demon.
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He will ask you to get a broken piece of a seal from Bear in Battle (Disciple of Brotherhood of Thieves)



Show the piece to Monstrous Soul Demon to complete the quest.
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He will give you 1 Black Moon Backpack and 1 Purple Bamboo Leaf and 1 Piece of a Seal found by Heavenly Demon.
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NOTE: To make easier the quest I add the map of the 4th level with the locations of NPCs.