Monster Girl Quest/WMG

Ilias is
To elaborate, it's just a way to see their relationship.

And yes, I'm aware this would mean

Luka is short for
There are a lot of implications that Luka is a, so why not this one?
 * Is? Or is
 * Potentially massive spoilers -
 * So Micaela woman in Enrika is Archangel Michael?

With the above in mind, Luka is either the Founder or one of his/her/its descendants
Alice claims that the Founder, who created all monsters, has been missing for some time. There are many suspicious details regarding Luka's birth, such as his mother's ring and her apparent connection with the game's Hidden Elf Village. Then there's his incredibly powerful abilities he can only use when asleep or otherwise unconscious. Regardless, Luka is certainly not a normal human.
 * Plus, he is gathering the artifacts necessary to create something called the Holy Wings.
 * Only in optional sidequests, so these Holy Wings shouldn't influence the main plot.
 * Perhaps they are needed to avoid a Downer Ending?
 * The Holy Wings part is debunked by second episode, the Orbs are used to summon Garuda.

Ilias is evil, the game will end with a confrontation between Luka, the Monster Lord, and her.
We've received multiple hints that Ilias is not as benevolent as she appears. She is planning on destroying all of the monsters, her "teachings" are her ways of weakening them before she strikes the final blow. Luka is following her teachings with less enthusiasm as it is, and is even starting to doubt her by the end of part one.
 * But then who will man the Assessment Corner?
 * Amira, naturally.

Ilias is a Chessmaster extraordinaire.
The plot of the game is based around her commanding Luka to "defeat" the Demon Lord, not kill her, and Alice has said that only someone who does that can marry one of the lamia clan. Ilias is hoping, through Luka, to create a new generation of kinder, less hungry and  hungry monsters.

Alice will have to make the Sphinx's Sadistic Choice
Its pretty clear that Alice is. Concerning the long lives that monsters live, she, {{spoiler|or Luka]] will have to make one of the three choices. That is, unless {{spoiler|Luka really is a Fallen Angel}}.
 * I wouldn't say she's {{spoiler|"grooming him to be her husband"}}, it just seems more like, in classic Tsundere/Kuudere fashion, she's falling for his inherent goodness and idealism despite herself. If she was actually "planning" that, the choice wouldn't be very dramatic because she would have already accounted for it. But yes, it will highly likely come up again later.

Luka will have access to a Harem End, including all the Knights
Why else give him the Dragon Crest?

Luka may have his choice of the Knights to end with
To go with the above. Furthermore, Alice and the Knights are the only voiced characters, as well as most of the monsters (Harpy Queen, Sphinx, and Kraken the only other examples) that seem more open to reason than simply following their urges.
 * Confirmed... in a sense. In the epilogue, there are "endings", so to speak, where Luka gets raped by various other characters that he has met on his journey, including the Knights. The only proper ending (one that doesn't bring up a retry/title choice and actually has credits) is the one with Alice.

Ilias is YHVH

 * Her One-Winged Angel form will be a giant floating head.

The MGQ world is a Netherworld

 * And Ilias is the local Overlord.

Luka will get Unwanted Harem in third part

 * As demonstrate in the end of part 2, "earthly" monster can't harm angel at all. So it's up to Luka for bestow the monsters with holy power.

Sara will have an important part in the third game.

 * We have seen direct evidence that once a human woman is turned into a monster, the change is irreversible: cases in point, the Worm Villagers in the Witch Hunt sidequest and the Maccubus, Mincubus and Lencubus in Succubus Village (whose unsealing was admittedly accelerated by Alice's blunder). It makes sense, since Alice explicitly states that Angel Halo's sealing power will eventually wear off and the monsters return to 'normal', as seen when the Crab Girl from part 1 returns for a rematch in part 2. Sara, however, gained an immense amount of power from her succubization thanks to Sphinx's blood, even exceeding a Queen-level monster right off the bat, and her body prominently displays the same tattooed motif as the Four Heavenly Knights and Alice herself, meaning she became a monster of the highest order since no other monster displays those motifs on themselves besides the strongest. It stands to reason that she will get exposition due to this, especially seeing how she supposedly should have spent some time in the Monster Lord's castle with Granberia, who may well be the best person to teach her the self control she was lacking when she turned. This may well be a very important thing in the future.
 * Jossed - She does reappear in the third game, in the Monster Lord's castle, but employed as a maid.

Chrome will make Heel Face Turn in the third game.

 * And her research on ghosts will contribute greatly against Ilias, possibly allow Luka to contact with Heinrich, but more important - ghosts are no longer "of this Earth" and thus may able to fight angel back. Of cause, the main point of this is to scare Alice.
 * Confirmed, but not for these exact reasons. Chrome does return in the third game, with her own subplot revolving around her . Once that concludes, she will eventually join forces with the rest of humanity and monsters to oppose the angels.

Promestein isn't a true angel, she's human with artificial angel power.

 * Lets be Genre Savvy here, it's a little wrong to blame higher power for all evil, and as we known, humans are always the worst. That explains her unusual wings and halo. Most likely, she will take the role of Final Boss, after Black Alice and Ilias are out of her way.
 * Jossed. Promestein is a low-ranking angel who has been banished from heaven for making contact with humans. She is also one of the penultimate bosses, coming before Black Alice and Ilias.

Alice won't be fighting alongside Luka in Part 3, because she
They will have to find a reason, why Alice is not fighting in the game, even though the enemies won't be normal monsters, because in gameplay terms she is too strong. So why not prepare for ?
 * There's one very good reason for her to not fight: Monster Lord or not, she's still an Earthly monster, and Earthly monsters can't touch angels. At all. As such, given how angels are the primary opponents in the sequel, she'd be worse than worthless - she'd be a liability to Luka, as she'd be unable to do anything to them, and he'd have to defend her all the time. It's common sense, really... at most she'd be useful against the Chimeric monsters, but plenty of previews showed actual angels fighting Luka, and those, she's of no use against. Plus, Luka is already near her level anyway, and will likely surpass her in short order, so "too strong" is debatable.

On the elemental spirits and their children
When Micaela gives the backstory for the setting, she explains that there were two fundamental energies in the world (holy and dark), which gave birth to Ilias and Alipheese I respectively. However, as we learn shortly afterwards, they are not the only fundamental energies in the world: Fire, Earth, Water and Air are just as necessary to the continued existence of the world, and the death of their personifications would destroy the world just as readily. However, this leads to something weird with Sylph and Undine: Namely, they're fairly obviously a fairy and a slime, who are monsters, which are creatures sprung from dark magic, which is quite explicitly not the same as the elemental energies.

However, what if fairies and slimes aren't actually monsters? If the avatars of light and dark were capable of creating life in their own image, why couldn't the spirits of the four elements? It would explain why fairies and slimes have such odd traits (Being invisible to those with strong religious beliefs and being able to reproduce asexually respectively), and it would help whittle down the monster family tree to having only six ancestors. Salamander and Gnome are a little harder, due to their homes not having any specific type of inhabitant. Salamander could be the ancestor of creatures like the lava girl though, while Gnome bears some resemblance to an Elf, or one of the Brownies from Paradox.