Sanji is instantly won over by her beauty and grace.
Unlike her previous cold demeanor, Robin approaches the crew with a strange request: she wants to join them. She explains that because Luffy forced her to live during the collapse of the Alubarna Royal Mausoleum—when she had already given up on life—he now has the "responsibility" to take her in. One Piece (Dub) Episode 130
Robin wins over Nami by offering her a pouch of jewels she took from Baroque Works. Sanji is instantly won over by her beauty and grace