Trial key 5

[cluthz]

I'm missing trial key 5. After grinding thru the whole corridor several times I consulted some guides and they say it should be located in 3rd stratum, but after running thru 3rd stratum 4 times more I still haven't found the 5th key.

I'm at a loss here, are the trial keys missable? (I'm what I would guess halfway/near the end of the final chapter and I wanted to finish up things I've missed before the end.)

[Koby]

Trial keys are random chest items. You might have to run through the stratum multiple times.

Make sure to grab all chests.

Don't worry about missing things before the end in the Reverie as once you beat the main story, you'll have infinite time to do everything in Reverie during post-game and nothing is missable there.

[saviour]

I think they appear only in blue chests to be more precise. You can only target those ones to gain some time while rushing through the stratums.
And yes they aren't missable so you will find them as long as you continue playing.