The Familiar of Zero/WMG

Louise's spells have the side effect of making people stupid.
This explains why:
 * Louise's first spell is to summon Saito. What does Saito do the next day? He starts a fight with Guiche, and continues even when he's losing badly (he did win, but he had no way of knowing he would).
 * At his first appearance, Cromwell is content to wield his magic ring from the a safe distance, while he stays quiet. At the end of season 1, he gets a face full of Louise's stupid ray and starts monologuing in front of Tabitha and Kirche where Guiche can sneak up behind him with a big stick.
 * That spell might have had a massive AoE effect which made everyone noticeably stupider for season 2.
 * At the beginning of season 2, when Louise gives Saito the glasses, she blasts him over and over again. Each time, the very next thing he does is provoke her into blasting him again. When they see the princess, it's been a while since Louise blasted Saito so the stupid has worn off, making him at least smart enough not to look at the princess and trigger the glasses. When she does get him to look at the princess, she blasts him with an even bigger explosion -- which seems to knock even more stupid into Saito, whose next action is apparently to make a pass at the princess.
 * This makes so much sense. I love this theory.

Derflingher is a Zanpakutou
When Saito starts using it to absorb magic spells, that's because he just figured out how to release its shikai form.

Saito is Keitaro Urashima's cousin

 * And they both have similar superpowers: magical resistance to the Groin Attack and Megaton Punch.
 * And are both attracted to violent tsunderes.

Saito is a masochist
Back on Earth, he never had a girlfriend for too long because they ran away when he told them about his fetish. He doesn't tell Louise because he knows that if he does, she might stop.

Actually, this guess might not be wild enough to belong on this page.

"Semi-confirmed in the the 8th light novel (according to Baka-Tsuki translations, at least), with Saito's dream:"

"Tabitha remained expressionless, but like a machine-gun she spat out a string of words:

“Can’t find a boyfriend? Mind your own business! Stuck between the maid and the boob-less mage, you have no right to talk about me. Someone like you, all you need to see is the princess, the village girl or elder sister with big breasts and you instantly have that “look”, really a mess. Then you will say ‘no no, I can’t do this kind of thing, because I am from another world, so I cannot support your feelings.’ But while you talk, your body doesn’t react the same way.”

“You, You,” Saito’s head became red as a tomato.

“A person like you would seriously annoy them both, you make them want to come after you with violence.”

Saito looked at Tabitha’s height and replied, “You, you little kid, don’t talk so spirited like that.”

The girl’s was a head shorter than Louise, but Tabitha’s expression remained unchanged, and added, “Who is a kid? You are the real kid! A brainless person like you who tries to step into two ships with one foot, you are ten years too early!”

"Gya!"

Saito suddenly curled into a ball aboard the wind dragon. He had apparently been kicked in the groin by Tabitha. Then Tabitha followed it with a straight kick to Saito’s face.

“I should keep you as a pet.”

“Stop joking!”

“What are you talking about? Aren't you very happy? You like it, don't you? When a loli dominates you. It is written all over your face!”"

Other items from our world end up in Tristain
The people in Tristain, when they do laundry, end up with extra matches to their socks. When they look for their keys, they find extras. Nobody in Tristain makes wallets, because it's easier to find them lying on the ground.

's Holy Land is still Israel/Palestine.
Consequently, Brimir is not Magic Jesus, he's Magic Moses. We don't know how pimpin' Brimir was, else he'd be Magic Abraham. Brimi... Avram... crap.

On second thought, perhaps this isn't such a Wild Guess either:

"“Brimir is a god, I guess. Everyone, in Founder Brimir’s presence… starts saying prayers.” “Idiot. He is not a god. Brimir was a free person. No, not much… he was God’s spokesman… The nearest entity to it… I think.” “A great person anyway.” “That is right.” “Is this whole mess because this great guys' hometown was taken over by elves?”"

This goes with the theory that time passes in  Earth at the same rate as IRL Earth.

The Magic Academy knew from the very begining the Louise was a Void Mage
They kept it secret because 1) Without the Gandalfr she could not use her abilities anyway and 2) They felt that letting her struggle with ordinary magic would give her the humilty to use her powers responsibly when the time finally did come.


 * Or they just thought they had enough explosions and that this girl REALLY didn't need to know she could use countryside-destroying magical powers, along with a super-humanly powered Familiar.

Siesta is a ninja
Because she's 1/4 Japanese, courtesy of her grandfather, and because she's a maid. And as we know, all Japanese maids are ninjas. Gramps was actually Japanese special forces in addition to being a navy pilot (just go with it) and when he got stranded in Tristain, he decided to pass his skills on to the next generation to make sure his family would have some defense against these uptight "noble" folks. Siesta is very good about concealing her skills, so good in fact that she looked just like a Damsel in Distress when that Count Mott fellow tried to buy her contract and turn her into his concubine. When Saito came riding in to the rescue, all he really did was save Siesta the trouble of putting arsenic in his tea or her foot to his throat.

is the author's way to get a BDSM story past the radar.
Because it would not have an anime adaptation if it's Darker and Edgier.

on the other side of the world is Codex Alera.
Fury crafting is just a different type of magic, its been confirmed in the Codex that the people and some of the Critters are from other worlds, like how stuff from are world goes to  world.

Of course this means the Vord are coming, to eat them.