So in Phineas and Ferb "Isabella and the Temple of Sap," Isabella goes into "Phineas Land" (as she calls it), while Phineas is talking to her and she imagines Phineas into a minotaur who picks her up and rides away over a rainbow with her on his back.
So, if your OC were to have a (possibly completely unreasonable) daydream about their crush what would it be? (again, sfw only. I can't stress this enough.)
Jinwoo (of "Hushabye Prince") would (if he isn't already) totally imagine Kimberly as a princess in a huge ball gown, with a tiara.
Alicia (of "Damsel in the Red Dress.") is pretty reasonable, but she does somewhat imagine Kattar as her Prince Charming, like the hero from a movie coming to rescue her when she's in her lowest moments, but it's never, suddenly wearing a leather jacket and carrying a machine gut beating up all the baddies and then coming to carry her away in her arms level of daydream. (okay he is wearing a leather jacket, but he already had that.)