Earlier installments in the story were sadly rushed due to Executive Meddling, so the creators tried to release supplementary story material that they'd wanted to have in said installments, but had never been given the chance to actually add in.
The makers of the game thought that including too much plot in the game would slow down the fast-paced action they had in mind, so they put most of the plot's details in the manual.
The game was made during the early ages of video games where there wasn't enough room for a grand story. So only the important parts are added while the supplementary material went into the manual.
The fantasy novel Troperia Chronicles come with a CD containing a mini-game where you play the final battle between Alicia the Chosen of Light versus Empress Eviliss.
The Official Guide contains only six words regarding to the game's lore: "All there in the disc itself."
It seems that the main plot of Troperia Chronicles is barebone... until you play each character's optional sidequests.
Or the Troperia Chronicles game gets a re-release and has all the missing plot information intact so you can just play the remake instead of relying on Supplementary material.
Double Subverted: But to understand why Alicia must defeat Empress Eviliss (who was Virgilia), you need the Troperia Chronicles Official Guide.
The game contains nothing; everything is in the guide.
Important information is deliberately not revealed in-game, the characters complain bitterly and accuse the developers of trying to flog strategy guides.
Some of the story happens in-game, but some important parts are explained in the guide.
The game series is unfortunately an offender of retcons and other issues such as Continuity Snarl, so you can't be really sure if the supplementary material is accurate anymore or not.
"Selling the game won't even cover the development expenses, so let's put all the stories inside the Official Guide... which we will sell bundled with the Alicia figurine."
"Hmm... these Supplementary story materials are getting popular. Quick, let's make something like that for this series." "But sir, we never really had all that many ideas for this series' storyline before." "So what? Just make some stuff up and have in an "official" guide from us. The fans would never want to refute it, since it came from us."
Lampshaded: "My gods, Lady Alicia. I don't even know what's going on anymore. I pity the future historians who will study our era from what scarce texts there will be."
Invoked: Before the game begins, it has a disclaimer reading, "If you want to know more about the lore of Troperia Chronicles, please read the manual."
Troperia Chronicles has every little bit of detail in the game, making it overly long.
Word of God - "Hey, let's be honest here: we never really cared about storyline structure in this series, and if we act like we do now chances are this will most likely just make you guys more confused, so at least we're being honest about the lack of continuity here."
Discussed: "Hey, don't you think that we know very little about Lady Alicia? I think we should steal and read her diary."
"Wait, why did Lady Alicia do that?" "It's in the manual, actually." "I don't want to pay that much just to know! Curses!"
The heroes write a journal of their adventures, and, once they've won, give it to a historian who'll hopefully save it for the distant future.
Not many people play Troperia Chronicles, hearing about how it lacks any worthwhile stories.
The supplementary storyline material tries to be the Reconstruction but ends up being the opposite, and has all sorts of plot holes, raises more questions than it answers, and is filled to the brim with bad writing.
The storyline from the guide helps remove the majority or entirety of the problems in the games' storyline by removing plot holes, adequately answering any Fridge Logic questions and simply making the story appear to be better.
A fan translation of the supplementary material is released.
Played For Laughs:
On the game disk is the entire story played out like a movie, and the guide acts as a choose your own adventure book filled with nothing but action.
Or the series gives itself some Self-Deprecation for being a case of this trope, especially if any of the supplementary story material doesn't seem to make any sense combined with what is actually in the story.
Played For Drama: Empress Eviliss destroyed your hometown, but the game doesn't tell you why.note (She was forced to do so to create a rune that would keep out the demons.) During the game, you have several chances to prevent her from destroying other towns, or just saving the populace. Later, after you've stopped her, she activates a spell which summons terrible creatures that destroy nearly everything.note (By letting her destroy the towns, you could have prevented the disaster, but you would only know to do that from reading the "ancient scroll" that came with the game.)