On the top left of the nature dungeon (cannot remember the characters name) she is the leader. She will give you the special option, I can't remeber what triggers it, I think you have to beat all the bosses each before you get the option, I was also pretty leveled up. My team was Ryen, Chiyo, Mira & Mirel. It can be a slog but sometimes you get a break (I did it a lot) Good luck.