[Hayashi]

Did you consult the journal? It will have sufficient leads to enable you to solve it on your own.

(Spoilers)
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After meeting baron Ployer at the Sea Bounty's Inn in the Docks district, go to the Copper Coronet and talk to Bernard - he'll give you some information.

You could then go directly to the "Derelict House" in the same area (The Slums) and confront Ployer. But if you do so you'll have to contend with those mages that Ployer hired.

If you'd rather not face the mages, take a trip to the Government District. Enter the office and speak to a mage (Corneil?). He'll deny all knowledge of it, but when you exit the building a mage will come up and speak to you.

You have 2 choices. You can either bribe them to:
a. Kill Ployer, or
b. Stay out of the fight with Ployer.

Then go back to the Derelict House in the Slums and confront Ployer. Depending on your earlier choices, the amges will either fail to turn up or will teleport in and kill Ployer.

Once Ployer is dealt with, the curse has been broken. IIRC ja's lock of hair (which was what Ployer used to curse Ja in the first place) will be in your inventory. Then you will need to rest for three consecutive 8-hr periods (IOW, a full day) and Ja will be well.