The first problem with this one, is, of course, the song. The Hilary Duff song. Songfics alone already make me want to spork my eyeballs out. However, the way in which the story pieces match the lyrics, and the way in which they revolve around the excerpts are great. The story pieces themselves are awesome, clever, and unusual, especially the Petunia and Lily one, and it's not often there's an Arabella Figg fic out there. I wouldn't change the song or its role.
The A/N about the Hilary Duff song should have gone BEFORE the "SOMEONE GIVE A ME A SUGGESTION FOR A TITLE! I'M SERIOUS!" and disclaimer. As "SOMEONE...TITLE" is the working title for this fic, as soon as it's up the story has begun. No in-story A/Ns.
I'm not sure what the ellipses are doing instead of apostrophes in many of the contractions, but it's odd.
In the song lyrics "Cause perfect didn't seem so perfect" and later in "Cause I wanna feel the thunder," "cause" should have an apostrophe in front of it, since it's a contraction of "because," not "cause" like "cause and effect".
No A/Ns in story!!
"Planet Earth" is kind of vernacular sounding..."The planet Earth" is more appropriate here.
The stars, hiding behind Earth, had formed a neat line. The stars were neurotic and liked everything to be neat. So instead of clustering in a great big glob behind Earth, they formed a neat little line. The stars had to move along with the Earth to stay hidden.
Strike out "neat" in the first sentence. Lines are inherently neat, don't be redundant. Add a "like they normally do" after "So instead of clustering...behind Earth" to establish that they decided to change something. Otherwise the fact that those were the only two choices and there was no preceding state feels wrong. That last sentence is redundant. I assumed the stars, having been established as hiding behind Earth, would have to move with it to do so.
The earth, sun and stars were aligned in a perfect line.
Redundant sentence, and also redundant with in-sentence word usage. "The earth, sun, and stars were aligned perfectly" would be better.
Petunia saying "duh" jars. She's prudish, not sassy. Not to mention five years old.
His eyes widened. Wait, what was he thinking? He LOVED rain. Especially the 'dancing the weird insane crazy stupid loony dance' part. He jumped out of bed, rushed down the stairs, flew through the front door, and into the pouring rain.
'dancing the weird insane crazy stupid loony dance' is unclear until you read the second sentence. Should be 'dancing the weird insane crazy stupid loony dance in it.' Strike out ", and" from "flew through the front door, and into the pouring rain."
::Let it wash away
My sanity::
Of course, there was little sanity left in the kid to wash away. Not the 'suicidal sanity', but the 'weird hypocritical sanity' Or 'insanity'. Take your pick.
That makes no sense. First of all, those never struck me as being types of sanities, and in fact they make no sense that I can discern. If you want to say he was quite insane already, then say it. Brevity is the soul of wit. Secondly, is this the kid that ran out into the rain? Before now, every break between lyrics was about a new kid, so you must clarify the change in pattern. Also, it REALLY needs to be clarified if, judging by the "elegant hair" description, that was Sirius. Characterization much? It may be AU, but don't reference characters off-handedly with an "of course" by their new and unfamiliar personality traits, because then the readers are like, "Wait...who? Am I supposed to know this?" and it jars the mood. In AU you have to explain everything that been changed and to what extent, otherwise we assume canon.
He also knew of his other, very humourous, weakness.
Regulus then sneaks up on Sirius and shouts "WAKE UP!" at the top of his lungs. Now, what fear of Sirius's would that be? People with no fear at all are going to jump up in surprise if some sneaks up on them and shouts. It would be better if that sentence was replaced by a "Just then he got an idea" type of thing.
Again, no in-story A/Ns! I know Sirius didn't like his family too, but by the time we get to your A/N Sirius's new characterization and the interactions between the two boys have already established the difference and your A/N is kind of "duh." And the next A/N just sounds clueless, because even I can figure out the gist of those lyrics. If you just leave the A/N out, some part of the reader will be complete the pattern that the earlier bits had and find the "clean" reference in James trying to brush his hair. The readers are trusting sheep...if you continue a pattern, they'll assume it's there (and find one subconsciously), even if it's not immediately obvious to them, so it's more interruptive to put in the A/N.
The formatting of the Rebecca and Father dialogue is weird. I'll chalk it up to ff.net doing wild things, but it is pretty hard to read, between the symbols and lack of quotations marks and ellipses where apostrophes ought to be.
There was a scream. In the next thirty-seven seconds, several things happened at once:
Arabella, sorry, *Ara*, shot out of her bed at light speed.
She nearly bowled her dad over.
Rebecca ran as fast as she could as soon as the second-last syllable was out of her mouth.
Ara chased Rebecca.
Philip went down to eat his breakfast, which his wife, Janet, had made.
Rebecca almost didn...t make it.
Ara almost caught Rebecca.
Downstairs, Janet turned on the radio.
Rebecca slammed the door.
Ara nearly crashed into the door.
Ara grumpily stomped back to her own room, found she couldn...t get back to sleep, cursed Rebecca under her breath, and went to brush her teeth.
In her room, behind the locked door, Rebecca grinned.
First of all, I'm not sure why "Isn't it a great day to be woken up at nine in the morning" would cause Arabella to scream and jump up and chase her sister around. I know I'd sink even deeper and more determined into the bed. So I'm not really sure what instigating event this chase scene is the result or resolution of, and a good instigation is a big reason why chase scenes can be fun to watch and get tense about and root for. Also there was a lot of needless information there, with the whole Janet/wife thing and Ara as a nickname. Ara is a bad nickname anyway. It should be Bella or Ella. Also, no introducing nicknames in the narrative. The characters should be able to establish the nicknames themselves, and as Rebecca had already called Arabella by her full name, it should remain that way. Also, that list was supposed to be several things that happened at once, at the same time. So that means that as soon as there's an event that is not happening simultaneously with the others - sequentially, in other words - the list should be ended. So as you've no doubt already guessed, the list was way too long, filled with redundancies and too many items. Observe:
In the next few seconds, several things happened at once:
Arabella screamed and shot out of her bed at light speed, nearly bowling her father over.
Rebecca's voice died on the second-to-last syllable, and she began running as fast as she could.
Before the covers had time to settle properly, Arabella chased Rebecca from the room and into the hallway, the younger sister shrieking in excitement. Philip followed, but in his own time; he quietly shut the door and shuffled downstairs to eat the breakfast his wife had made that morning. Upstairs, Rebecca almost didn't make it - at one point she could feel Arabella's fingertips catch on her flying hair - while in the kitchen their mother turned on the radio. Rebecca's feet pounded towards her sanctuary, her breath coming in tense, involuntary gasps, half heaving gulp, half laughter. Her room drew close. She hurtled forward and swung towards the open entrance, skidding on the carpet but remaining miraculously upright. Once across the threshold, Rebecca whirled about and slammed the door, forcing her sister to throw herself sideways to avoid crashing. Arabella growled incoherently at the doorway, but gave up and grumpily stomped back to her own room. After discovering that she couldn't get back to sleep, she cursed Rebecca under her breath and went to brush her teeth.
In her room, behind the locked door, Rebecca grinned.
Hardly perfect, but much improved.
Anyway, that's an as-I-was-reading-it review. Since you asked for one.