I have just started Chapter 4 and already have gotten all the other Summons apart from Deus Ex and Susano-o.
reading Mephilia's notes D's Journal i can guess Deus Ex is where the Earth Crystal is (the tower that used to be the Earth Temple) and Susano-o is somewhere on the crescent island at the top right. i took Grandship there but i can't find any place to enter, i even dropped the smaller airship into the water and sailed around the center island.
I did try looking at the small islands around crescent island but i can't see anything apart from a small obelisk like object south of the island in the Florem area which i can't enter
So how to i get Susano-o? do i need to get all the other summon's first before it's possible for me to get Susano-o? or is the start of Chapter 4 too early? (since i won't be able to get Deus Ex until much later)
Best Answer
You can get Susano-o as soon as you get the airship (so before or or any time after Chapter 4). You can possibly go even earlier with the boat but as it is a strong spell you likely will not survive at an earlier point.
You do not need the rest (or any) of the other summons before they will show up.
They are in the top left corner of the crescent Island.
There is no other indication that they are in that location. Supposedly you are able to just walk into that spot and it will start automatically as well. I just got lucky with my airship.