Content Type: Gaming Guides
The Magus Sisters are one of three optional Aeons that Yuna can obtain, and are the strongest in the game. You can acquire them after you recruit Yojimbo and Anima. You will also need the items 
Flower Scepter and Blossom Crown to get them.
Flower Scepter
To get the Flower Scepter, go to the Remiem Temple in the Calm Lands and you will find Belgemine. She will challenge you in a battle with every Aeon that you’ve obtained, and you must fight her Bahamut. Once you beat him, she will reward you with the Flower Scepter.
Blossom Crown
To get the Blossom Crown, you must do some of the monster capture side quest in the Monster Arena. Capture at least one of every fiend at Mt. Gagazet, and you will be given the Blossom Crown.
Obtaining the Magus Sisters
Once you have Yojimbo and Anima, and have gotten the Flower Scepter and Blossom Crown, make your way back to the Ramiem Temple. The door behind Belgemine will now unlock, and you can enter it to recruit the Magus Sisters.
Obtaining the Magus Sisters will earn you the achievement ‘Delta Attack!’
I have fight every Aeon,Anima & Yojimbo included, I haven’t obtained the Scepter, fuck
That’s really weird! It’s not showing up in your Key Items? Do you remember what it said you got when you beat Bahamut?