You need the Flower Scepter and the Blossom Crown.
To get the Blossom Crown you need to catch all the fiends at Mt. Gagazet/ Calm Lands Area and then talk to the Monster Arena guy. Don't forget you need the special weapon to catch them. To get the Flower Scepter you have to fight the summoner in Remim Temple, after defeating Valefor all the way through to Bahamut, she will give it to you, don't forget you have to win the battle.