Yo friends, currently planning for the effect overall.
old
Main ref. FF8 Diablos summon
https://imgur.com/a/QZ2mABE
1 - Mesh dissolve into Bats
2 - Bats form a sphere
3 - Mesh Get out like Diablos
4 - Give the mesh some kind of powerup, like an Aura or what
main ref: https://www.youtube.com/watch?v=T7EXeQyuHbI
effect atm:
I will mash that square button to boost your success on this!
Some iterations later, i got something totaly different 
main ref: https://www.youtube.com/watch?v=T7EXeQyuHbI
still a lot of work to do
more energy in
destructive ground
explosion at the end and want to give the mesh at the end a powerfull buff that feels good
Evolve into a Demon
i feel like its missing something…
I love it! Maybe add a nice groundcrack add the end after the orb explodes 
I think the effect is interesting, but because if your choise of colours and shapes, it feels more like a princes suit up effect then a demon evolving effect.
There is magical fairy magic flowing into a light emiting shape, and when it is finished, flower petals fly out
To help this, try adding darker colours into the effect, maybe add something that reminds one of blood?
Also think about shapes, try making things spiky instead of flowy, harsh instead of soft.
Do keep the aftermath aura though, that adds a very nice touch.