Fanfictions based on "Marauders, Lily, and whoever else read Harry Potter 1" are unoriginal and use a minimal amount of original text. See, look:

The Marauders were sitting down when all of a sudden a magical book fell through the ceiling. Instead of check if it was hexed, jinxed, or cursed, James opens the book and reads it.

The boy who lived blah blah blah there was a woman blah Dursley blah blah blah Potters suck

"Hey!" even though James was the one reading the book, and therefore, based on human psychology, shouldn't interrupt the story, he yelled at a book. What a genius. "Potters don't suck!"

Then James said something about how Lily married him, but no one cares because everyone who would be reading a story like this would already know.

Then everyone makes guesses on what characters say, and who they are, and somehow, they all guess correctly.

A cat sat stiffly on the wall. blah blah brick wall blah blah.

"HEY!" said James, once again interuptting his own story. "IT SOUNDS LIKE AN ANIMAGUS! IT MUST BE PROFESSOR MCGONAGALL BECAUSE THIS STORY HAS TO HAVE AT LEAST ONE CHARACTER GUESSING ANOTHER IN THE BOOK!"

Blah blah blah. Story blah blah Harry potter lived blah omigosh he is a living boy blah

Now everyone was yelling at the book "BLAH BLAH! MUGGLE IS BLAH BLAH! WHAT AN IDIOT BLAH BLAH!" And even though these people could have been fictional, they automatically assume the book is from the future and these things are really happening. After a while, they say things like 'isn't Quirrel that nervous Slytherin dude?' or 'I know the Rowlings! They are an ancient group of purebloods!' and other cliché things like such.

"Hey, isn't Quirrel that nervous Slytherin dude?" said Remus, giving another random fact that we all don't need to know.

"Yeah!" said Lily. "And Mr. Dursley is Petunia's fiancé! And Harry is what we're going to name our child! And (blah blah blah blah blah, more random facts blah blah blah!)"

Then:

BLAH BLAH BLAH! MOST OF THE STORY IS TAKEN UP BY PLAGIARISED TEXT FROM HP BOOK ONE, AND SINCE YOU PEOPLE OBVIOUSLY WANT TO HEAR FICTIONAL PEOPLE'S REACTION TO READING A BOOK AND SHOUTING AT IT, HERE IS THE STORY BLAH BLAH. BLAH BLAH —

"Blah, blah?" said Sirius. "Blah blah! Disagree blah blah blah! What is a drill blah blah blah!

BLAH BLAH BLAH! BLAH BLAH BLAH—

And every once in a while —

And since we all know that wizards are freaks —

"HEY!" everyone shouted, even James. They all had been offended by whatever was in the book. After all, JK Rowling's, a woman who they didn't even know, opinion was so important to them.

"This book has said a phrase that I don't like and now I am going to not read it because this book has caused me great stress and anger because everyone knows that fictional books make people angry." Said James, and left the room.