The mask of gu is a part of the cosmetic Gu outfit from the player-owned port minigame. It is obtained from a Gift of Gu chest after giving a donation to the Tengu after completing his final clue voyage.
Each chest donation has a chance to provide a parcel with a random reward, but a donation of 25,000 chimes will guarantee a parcel containing one of the Gu cosmetic items that the player does not already own.
The Gu outfit pieces are received in the following order: Gu hakama, Gu uwagi, The Way of Gu, and lastly Mask of gu.
Players who have completed all of the Tengu's player-owned port clue voyages and have received a Mask of gu can purchase the Sojobo Contract Guru unlock from the Waiko Reward Shop for 100 chimes. This unlock halves the cost of re-rolling Arc contracts. This unlock is required for the Salty title.
For an exhaustive list of all known sources for this item, see here
- ^ There is further information on this drop; see the associated page for details.
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