Exaggerated: The steps to getting Persephone are: talk to two random NPCs, go to three certain areas, check an object too early, listen to a rumor, and take Olivia. As well as that, let some party members have a fight with someone, talk to another person who isn't so random, continue through the game, and wait for the event to be triggered. None of this is hinted at anywhere, making a massive Guide Dang It.
Downplayed: In order to unlock Persephone, Olivia must be taken back to her home town from near the begining of the game. It's well known that Olivia is from there, but nobody actively says they should take her back there.
Justified: The events to getting Persephone lead in to her arrival.
Inverted: A monster which needs to be obtained, and can be done with relative ease, to advance the plot.
Subverted: Olivia says she's always wanted to see Persephone when you get her.
Double Subverted: But she always says that about the other mons you can get.
Parodied: To keep Olivia alive you have to use the "chicken dance" action from the menu 100 times with her in the group, and she starts danceing with the message "Olivia has joined the party".
Zig Zagged: ???
Averted: All monsters in the game are obtained easily.
Enforced: Olivia is hated by most other developers so they made it complicated to keep her.