Find Strahad Farsan in Ratchet.
I have taught you skills in the past, but the time has come for another to teach you. He is in Ratchet, and his name is Strahad. He is human, but do not let that fool you into thinking he is weak, nor is he your enemy... at least for now. He is powerful and should be respected. He can teach you about greater summonings, summonings I feel you are prepared for. Go to him now.
You can find him in Ratchet... above the port town next to the tower there.