The "companion selection screen"
Initially I thought that the two selected characters would determine the available creatures to summon+spells. But this way, would mean that the Death creatures would ALWAYS be present (since both main protagonists are death avatars).
So the options are two:
1) allow to choose both the two characters, which means that Lily/Ace could not be present
2) the chosen ally would determine only the spells (the spells are cast by the avatars and are unique to each), but the creatures would be choosen in another screen
I went with option 2, since the first one was a bit weird (the main character not present in the fight). Besides I think is better if you can select the elements separately in another screen. I am even thinking if to just have a sort of "roster of available creatures", each one with a value (based on the level/power) and you can spend "Soul Points" to choose which creatures will take part to the battle.
As you can see, there's still a lot to brainstorm
And also there's not a right or wrong choices, all the various combinations could be interesting to play, but "sadly" I have to pick one