Kore wa Zombie Desu ka?/WMG

The other zombie is in fact Ayumu from the Future.
He has white hair, yellowish-brown eyes, cooks. Seem like a jaded version of Ayumu

Ayumu is only convinced that Yuu has a dere side because he is under her spell.
She is a necromancer and raised him from the dead as a zombie to do her bidding. He is mentally bound to be loyal to her, no matter what. To rationalize his behavior he is convincing himself that she is secretly a really nice person. Maybe the delusions he has about her acting cute are even what he actually sees when she shows him notes with her commands.

The 'Serial Killer' Ayumu is looking for is the Vampire Ninja in the OP.
She wields the same kind of katana that Ayumu was impaled with, plus she is clearly shown fighting him in the graveyard in the trailer to the series.
 * Pretty much debunked by now. Sera's katana is made of leaves, not metal.
 * Completely Jossed as of ep 5.

Ayumu is actually Keiichi
He looks exactly like Keiichi, gets dressed in girls' clothes, and. It would not be surprising if Eucliwood Hellscythe and Hanyuu are good friends.

Haruna is Cute and Psycho

 * How else will you explain her resemblance to Rena of Higurashi and the fact that she uses a frigging chainsaw as her weapon!
 * And yet, at the same time she bears more than a passing resemblance to Hayate Yagami of Nanoha fame.

Kyouko will come back, possibly as another undead.
She is featured in the Freeze-Frame Bonus, so either there is something very important about her suicide...or she's not gone for good.
 * Yep, she's important.
 * Following on that, next prediction: Yuu breaks out the scythe next ep, and we get to see exactly WHY she has so much respect.
 * Nope. She pulls out no weapons, for she needs no weapon but her voice to kill you. She then proceeds to do so. Several times.
 * Confirmed as of Season 2. She makes cameo appearances while "jailed" by Dai-Sensei, then gets to spend a lot of time with Ayumu in episode 8. She's just a normal Masou Shoujo though, and still a bit crazy in the head. And Ayumu now has another haremette to add to his Unwanted Harem collection.

Kyouko is an Eldritch Abomination and a (literal and figurative) Complete Monster in its true form.
The end of episode 4 has Kyoko kills herself. She is killed by... something pure evil... that took her body. It possesses great power and overpower the protagonists and even Megalo.
 * So she's a witch now.

The Scythe Yuu has in the OP is a Red Herring, or just a Shout-Out to her name-Hell SCYTHE, anyone?
Basically, we'll never see it outside of the OP. Same thing goes for Haruna regaining her powers.
 * The second part of that (concerning Haruna) is Jossed as of episode 11.
 * Nope, in episode 9 her pen transforms into it.
 * The Manga states she has a Body Pillow Shaped like it on one of the random side pages in the Volumes.

Kore wa Zombie Desu Ka? Is an AU of To Aru Majutsu no Index
Think about it: Both protagonists are ordinary guys who gain an incredible power, and an incredible harem. They both fist fight, although one can cross-dress/transform into a mas(h)ou shoujo. The female cast members are similar, with Haruna and Misaka looking alike and being the tsunderes, Sera and Kanzaki being Tall, Dark and Bishoujo, and with Index and Yuu looking somewhat similar, and both being in a predicament where they cannot use their magic. Both series have copious amounts of fanservice.
 * I don't see how they are alike. For one thing Touma is implied to be born with his power and is actually considered someone that is extremely important to the Big Bad plans therefore he cannot be defined as ordinary no matter how much he claims otherwise. Ayuma is born a normal human that got his power through Yuu and the villians only want to get to Yuu through him. Also even though they both use fists they have different styles with Ayuma being a Lightning Bruiser and Touma being a Barrier Warrior that has a useless power against something not supernatural. The harem looks similar but their personalities are actually very different. Not only that their overall plot cannot be considered similar at all. The fanservice is there but every anime has fanservice.