Which extra scene are we talking about here? The one with the question mark?
The second Midnight scene will be unlocked if you arrive early enough to rescue her during the mall rescue section (she went home with you instead of going with Eraserhead and other Heroes).
You need Jiro in your team AND sending Mei to look for Midnight instead of scouting.
In case you don't have one of the above, then you have to read the dialogues and choose the correct team composition at each choice.