did try all the key combination (X1,X4,X10 and X20) in both day and night. i guess i need to do chaos route and/or see other scene to use the keys
Before using some keys of destiny I had accumulated on a run, I decided to recruit every unit first to force the keys to give me the exclusive key of destiny units, but I became unable to use the keys.
I loaded a previous save and i could use the keys without problems.
I'm ASSUMING that the keys have certain pools
1x Pool, 4x Pool, 10x Pool, 20x Pool
The exclusive characters are part of the 10x Pool as far as I'm concerned, never have I drawn them from other pools, but i haven't unlocked every exclusive character so can't say for sure.
And while the exclusive characters are part of the pool, you can't use the keys if you don't have non exclusive units available to draw, I also think that once you draw or recruit a certain character from a key of destiny pool, you can't get it again using the keys of destiny even if you dismiss it, I'm not sure though.
So tldr: if you recruited everything, you are fucked and can't draw the exclusive key of destiny characters, I'd start over or load a previous save if i had one, not sure if this behavior is a bug and might be patched later or if is meant to be this way.
EDIT: The strongest exclusive key of destiny units are drawn from the 20x pool.