After defeating Crocodile, buy Nami’s Desert Dancer Outfit from the Nanohana shop for 500 berries. Help Toto dig three times in Yuba, then rebuild his bar with 20 Wood, 10 Beer, and 200 Berries. Visit the rebuilt bar during the day and choose Dancer Job with Nami; she wears the outfit automatically, and you begin with Sensual Dance.