There's actually two quests to talk to wavebringer:
1 - Shirataki Temple - after you summon and defeat him (Summoning the Spirits) the first time, he will reappear "cleaned-up" and you go talk to him and he furthers the side quest line wherein you purify the land, water, and wood of mooshu from the plague oni taint.
Every time you set foot in this dungeon area you will have to do the summon & defeat again to speak to him.
2 - after you have done shirataki temple you see him again as an npc quest giver in Village of Sorrow where he tells you to go convince Oakheart to come around.
Have you tried engaging the minions to bring him out?
You could also try:
--changing realms (if the game allows you to do this while in a dungeon) --mark your spot, leave the area, then return --ask another player who has not completed Shirataki Temple to run the dungeon with you
