I own one bed, one pillow, one blanket, one TV, one PS3, one set of sheets for the one bed, three controllers for the one PS3, multiple games, a couple of movies, nine shirts, seven pairs of pants, etc, etc. I do not own anything mentioned past this point.
Overlord of Zero
I feel I should explain before anything else. This would be based on a conclusion I came to after thinking about what is known about the Overlord world.
Thinking about what is said about past Overlords and the cycle that Overlords tend to go through, I came to the conclusion that the Overlord is, for lack of a better term, the Avatar of the world, in a similar manner to Aang and the previous Avatars. I know that Aang and the Avatars before him were all good people, and that the Overlord is decidedly not good makes the comparison hard to understand, but my thoughts are based on the differences between the worlds themselves rather then only the Avatars. Most worlds in fiction are made up of people who run the full spectrum from Chaotic Good to Chaotic Evil, the Overlord world does not have this setup, instead it has all the different shades of Neutral and then the various types of Evil, because of this the Overlord is needed to keep the world from becoming stale or imbalanced.
I know that there are "heroes" in the Overlord world, but think about their reasons for being "heroes". In the first game, the seven heroes that went to fight the previous Overlord were all in it for themselves rather then because it was right or needed to be done. Jewel is obvious, she's a theif, she wanted to loot the tower, the Paladin wanted to be rich and famous, Melvin wanted to find a way to live without having to work and gain a limitless supply of food in the process, the others were just as bad, like Jewel all the dwarf was interested in was gold, I don't really remember much about the elf, Khan, I think that was his name, was just there because Jewel told him it would make her happy, and the wizard was just hoping to gain more knowledge and power for himself. Of the "heroes" that were involved, the only one we don't know much about is the one that became the Overlord.
All of those "heroes" were to easily influenced by the previous Overlord for there too have any good in them from the start. Not one of them regretted their actions, abandoning the new Overlord, or the things they did after leaving the tower. They were, at best, petty, selfish Neutral people, at worst they were petty deluded Evil. The Overlord is the only constant and truthful individual in the world, he does not pretend to be good just because it will make people like him more, he does not act like his actions are anything other then what they are. Yes you can save people in the game, but the reason for it is not ambiguous, the Overlord saves people based on the phrase "That which does not kill you only proves that you are still of use to me." The Overlord is the only true Evil in the world, anyone else, even the Forgotten God, are just petty and selfish. There will always be an Overlord, what Gnarl says does not seem to be his personal opinion, he is just stating a fact "Evil Always Finds A Way." Without the Overlord the world would eventually fall apart.
Now, taking into account that the Overlord is a balance keeper, even if he usually isn't aware of it, I think it would be likely that the Overlord of the Infernal Abyss would have eventually figured it out, being stuck in the Abyss with nothing to do would get really boring so he would likely have began researching magic, the history of the world, whatever he could think of, when he wasn't torturing the souls of the people who betrayed him anyway. Eventually he would have come to understand what his purpose in the world had been, and he would therefore understand that balance must be preserved in all worlds, without balance the world will eventually become stale and crumble into dust, or be violently ripped apart by wars or wild magic.
Louise is a Void mage, but to be honest that title doesn't fit, saying that she, or anyone else in their world, uses void magic implies that they can just remove things from existence, since she obviously can't, that explosion is big and does a lot of damage to the area but it doesn't do anything that a powerful bomb couldn't accomplish, I think it's safe to say that her magic is something else that, for whatever reason, was mislabeled. The spells that they categorize as void magic seem to fall more under traditional arcane spell sets, or spirit magic, or dark, and a number of other types of magic, but they are not by any means void. Silence, the spell that prevents others from casting, is, to the best of my knowledge, an arcane spell in most fantasy games and stories, dispel is obviously an arcane spell since it works by unraveling the magic of other spells, and explosion is just that, it would normally fall under elemental magic, more specifically fire, but since it is just force, flash, and sound with no heat, it would also be an arcane spell.
From what I know, arcane magic is pure unrefined magic, it has not been changed by any outside force from its' normal state of being pure energy. Since it is clear that very few mages in their world understand what magic itself even is, it is safe to say that they would not understand the concept of unrefined magic, and since it is something they do not understand, of course they would think it is some mysterious, divine force. I think it is probable that what Louise's world calls void mages, are just people who do not have an elemental affinity, and therefore do not naturally and subconsciously convert their mana from pure arcane to one element or another.
Now that the main issues that could confuse people are out of the way, I can actually get to work on the basics of this little challenge.
The Overlord (you can name him whatever you want, as long as it fits) could have found a spell that would let him look into other worlds, it would basically be magic television, and eventually he found Louise's world. Seeing the state that the world is in, the Overlord would realize that if something isn't done it will begin to collapse, since he would have come to understand the need for balance, he would immediately look into the Overlord of that particular world, hoping that whoever it is will deal with the problem soon, since if one world falls apart it can have unpleasant side-effects on worlds around it.
The problem with Louise's world would of course be that there is no Overlord, and hasn't been since the Founder, Brimir having been the last Overlord of that particular world, though he didn't know it. The lack of an Overlord, or Avatar if you prefer, would be what was allowing the world to become unstable, the Overlord himself would want to fix this problem, but of course since it is not his world he has no way of interfering that won't make things worse, that is until his viewing spell finds the new Overlord of the world in question, though perhaps Overlass is more appropriate.
Louise has more potential then anyone else in her world, but because of incompetent tutors, and parents who don't realize they are doing the exact opposite of helping, Louise's magical potential is being wasted. Since they don't understand the nature of magic, everyone just assumes that Louise is a failure because she is different from them, the Overlord sees this and starts working on a way to somehow push Louise in the right direction, but before he can get far on that, he hears about the familiar summoning, and obviously any training he could give Louise would be much more effective in person.
When Louise performs the summoning the Overlord performs his own spell to redirect her portal to the Infernal Abyss. So Louise summons the Exploder of Melvin Underbelly, the Wielder of the Paladin Mop, the New god of the mumblers, the Purger of the Perverted Paladin, the Bully of Jesters, so on and so forth, you get the idea, she summons the Overlord of the Infernal Abyss, Slayer of the Forgotten God.
Once that is dealt with, and he gets her to understand that he is there specifically to teach her, the Overlord should not outright explain the situation to Louise, mainly because she wouldn't believe him at first, but also because it's hard to focus on learning when you know that your world is only a couple of years from going up in flames, or other natural thing scaled up to apocalyptic proportions. The Overlord can teach Louise to properly use arcane magic, though he should not explain that what he is teaching her is what she knows as void magic, again the whole denial problem. The Overlord, and eventually Louise, can cast pretty much whatever spells you want, anything from Fireball to Summon Infernal, necromancer spells from Diablo, the mage spells from WoW, and any other spells from WoW for that matter, they could use Dragon Age spells to if you want. The point is that this is the Overlord teaching Louise to be an Overlord, even if she isn't aware of it at first.
Louise does not have to be evil, different world different rules. Louise can, because there are already evil people in the world, be a good Overlord, although with the way she was treated growing up it would not be difficult to imagine her going off the deep end and reducing a few people to puddles. Louise can basically act however you want, the Overlord would be a little bit harder to work with since he has to make sure Louise is able to maintain the balance of her world, he is still the same guy from the first Overlord game, it doesn't matter how you played the game, his actions and behavior are still evil, he can change even if it is only a little, but no matter what he will still be the Overlord. I'm sure someone could make this work, just remember that the Overlord is there to help Louise get stronger, he should not be constantly saving her from everything, she needs to learn to do things for herself.
There will be no minions in this story, unless you can come up with a way for the Overlord to create them and bind them to Louise, this includes the Hives. Louise can learn to summon elemental's and demons, and even how to bind animals she encounters to serve her too.
Besides teaching her magic the Overlord should also teach her to fight, she will obviously argue, but that is a good reason for the Overlord to demolish Guiche in the duel without using magic, if he can easily take down a mage without using any magic himself it will make it clear to Louise that she can't rely on her magic all the time. The problem I have in regards to Louise learning to fight without magic is what weapon would be best suited to her, obviously a broadsword is out, and anything to heavy wouldn't work either, I was thinking a rapier or something similar, fairly small and light but quick and graceful enough to make up for the lack of physical power. If anyone decides to take this as the challenge it is meant to be, you can do whatever you want but it should make sense, I can't see Louise using a bastard sword, okay I can but it looks ridiculous.
Louise should be taught to cast without a wand, what good does it do a mage to know every spell in the world, if they can't use them without a focus of some sort? It would make for amusing situations where everyone loses their wands, or staff, and then Louise just starts flinging spells around without even giving the enemy a chance to gloat about them being helpless. The Overlord should never be helpless, and to insure that Louise is not, the Infernal Overlord would do everything he could to make sure she had the means to defend herself even if she is unarmed. Besides what I have already said, I think that the wand would be part of Louise's problem, it acts as the focus for her magic, and since she always tries to put more power into a spell then it actually needs, she is basically trying to force ten, or more, gallons of water through a normal straw all at once, hence the explosions, any substance, even energy, under extreme pressure has a tendency to blow up.
Besides normal spells and direct combat, the Overlord can also teach Louise enchanting, I mean the sort done in WoW and Diablo, making and using runesand gems with different effects being put into slots on items, they could even modify Louise's clothing so that she could slot gems and runes into her uniform. They could disenchant magic items for the raw materials to make more powerful items. Since I just mentioned clothing, the Overlord should bring some gold and jewels with him from the Infernal Abyss so that he can buy various things he may need to teach Louise, something he should buy as soon as possible is materials to make a duplicate of Louise's uniform that looks the same but is made of much more durable fabric, he should also get a weapon made for her and maybe some hardened leather armor that can be easily hidden under her uniform.
The Overlord should not be in full Arcanium armor, while it looks awesome and would definitely reduce the willingness of people to criticize Louise, or the Overlord himself, it would slow him down and attract a lot of attention he wouldn't want. Instead of full armor, I think a combination of the Arcanium armor and the Armor of Altair, from Assassins Creed 2, would be good, you can of course go with whatever you feel would be best. Since we don't know what the Overlord looks like, you can describe him however you want, but he should at least look human, no horns, or pointed ears, or fangs, that would just be silly. (If I spelled the magic metal from Overlord wrong feel free to correct me. What sort of weapon the Overlord uses is up to you, though personally I prefer the sword.)
When he first arrives, the Overlord should set up a spell to slowly draw magic from Louise, and from other sources, to create a Tower Heart, the spell could also siphon the excess magic from her spells until she learns to put the correct amount of power into a spell. It would take time for the Heart to be big enough or powerful enough to "Grow" a tower but they would have time, and given the amount of excess magic Louise tends to give off, it would probably be the same size as it was when the Infernal Overlord's son launched it at the Empires capital by the end of the Albion arc. What color the Heart is is up to you.
There can, and probably should, be some romance in the story, who it is between is up to the writer, but it should not be the main focus of the story, more of a "side-quest" then a plot point. The Overlord may be much older then any female character in the world, but age differences have never stopped people from using a pairing before, besides he would at this point be effectively immortal, so age really isn't the issue you should be having with the situation, if you have a problem with it at all.
I'm sure that I forgot something, or a lot of somethings, but for now I'll leave this as is. Thank you for bothering to read this, and feel free to make changes and use the idea, that is why I'm posting it.
Hob the Magical Robot