I've completed the shirataki temple quest twice, once for the initial quest, and the second time to read the book.
I'm going back again to complete the mossback quest, now that I understand his quests have to be worked in order.
Here's the problem - Mossback is sending me to talk to Wavebringer in Shirataki temple, only Wavebringer isn't there. There's a diseased water spirit in the courtyard where Wavebringer was the first time I completed the quest, but Wavebringer isn't there anymore.
If you've completed the shirataki temple twice, then you should know that you have to defeat Shoji to get the key in order to move the level that opens the gate. Then you need to defeat Haru in order to remove the barrier to the temple. Then you need to light all shrines in order to summon Wavebringer.