Basic Trope: Two characters get together for no reason with no proper set-up, so the relationship comes across as forced or contrived.
Roy gets together with Princess Missy, whom he only just met, with no explanation why.
Roy and Missy have known each other for a long time, but they have had no romantic interaction or even little to no direct interaction with each other until now, with no explanation why.
Roy and Missy do interact very frequently, maybe having romantic chemistry or a Will They or Won't They?, but when they get a Relationship Upgrade, it's done in a clumsy or poorly written way that doesn't make their getting together seem believable.
Exaggerated: Everyone in the series pairs up to no apparent rhyme or reason aside from the writer's whims.
Alternatively, Roy and Missy have plenty of chemistry; it's just offscreen. Whenever the hero is around, they don't speak with each other much, because the hero keeps them busy with other unrelated things. Once they finally do hook up, it seems to come out of nowhere.
Inverted: Roy and Missy have been together for a while and then suddenly start having problems and break up for good with no explanation why.
It looks like Roy is going to get together with Missy, as they were instantly treated as a couple for a while with no explanation, but then he actually gets together with fellow adventurer Jessica, whom he has a strong connection with and shares most of his interests...
Roy and Missy get together upon their first meeting but it is later revealed that they knew (and loved) each other as children and subconsciously remembered each other during their first onscreen meeting.
Double Subverted: ...but then abruptly dumps her for no reason and hooks up with Bob.
Parodied: Princess Missy becomes soul mates with the first person she points to, which just happens to be Roy.
Zig Zagged: Princess Missy rush to engage with the hero Roy, because it's how it's supposed to work for a princess. Until her mother explains her that it's just bullshit, and helps her to break the engagement and find a better suitor. When it comes out that Missy's loved one is an inferior workman, the Queen suggest her to just keep him as a secret lover, and to eventually marry Roy for cover. Princess Missy at first agrees, but later decides to neglet Roy to find an even better husband than him, until she finds out to be in waiting of the workman's child, prompting to instant marriage with the disponible Roy.
Averted: Roy gets together with fellow adventurer Jessica, whom he has a strong connection with and shares most of his interests, in a way that makes sense.
Lampshaded: "Hello, love of my life, whom I have known all of 25 seconds."
Invoked: Roy changes fate so that in an alternate dimension he and Missy get together for no apparent reason.
Defied: "How can you be madly in love with me? We just met this morning."
Deconstructed: The fact that Roy and Princess Missy hooked up without good reason leads to serious problems in their relationship later on.
Reconstructed: Roy and Princess Missy manage to work through their problems, allowing themselves to develop a real, solid love for each other.
Plotted A Good Waste: The two of them pairing off is part of a Bittersweet Ending; near the end, Roy acknowledges that he isn't really in love with Missy, but her kingdom needs a strong ruler to deal with the corrupt court, and he can't risk a Upper-Class Twit or Evil Prince taking her hand. The two agree to play a loving couple, and hope that time will bring about a true bond between them, but for now, it's more an alliance than real romance. The lack of chemistry between them was actually meant to be Foreshadowing to let the audience know something was up.
Played For Laughs: Two characters are literally forced together by a rope or chain and are ushered off to be together, despite their protests. When asked why, the only response they get is that it has to be that way because that's how stories end!
Played For Drama: A love triangle between Roy, Missy, and a legitimate love interest.