So the idea is the crystal bequeaths the powers of the summons to the humans it "protects" which is why during the gameplay you can see the hero project the Titan's gauntlets and the wing of Garuda and so on.The phoenix stuff interests me (obviously). I wonder if it'll be a ripoff of the X-Men Phoenix Saga, there's already some crystal mentioned in the trailer and if the phoenix is the guardian of said crystal then...
The Phoenix is the little prince boy (also I believe the little brother of the hero) who is, I guess, especially blessed, and outright transforms into a summon as opposed to being able to tap into a bit of its power.
This seems to be a bad thing for the kid and as an extension of that to the hero, who is seeking to end the crystal's protection. From now on this in an inference but I got the feel that they use the kids who turn into summons (there was that girl who I think was Shiva too early on) as living weapons and may even sacrifice their lives to turn them into summons, in any case it's not good for the kid to embody the full summon despite the military power it gives your nation.