Noctis falls in love Prompto because of the fact she is the only girl who not treats him both as a regular person and as an equal. He doesn't know how to articulate his feelings for her though until another guy at school asks her out and Noctis immediately pulls her away proclaiming she is already 'his girlfriend.'

How the rest of the story goes is up to the writer with the exception of two conditions.

+Bonus this gets out throughout the school immediately.

+Bonus Prompto (who loves Noctis as well) and everyone else wonders what he could see in a commoner such as herself.

(Whether or not smut is included is up to the writer)