Related to <a href='http://z14.invisionfree.com/The_Fanfiction_Forum/index.php?showtopic=20843&hl=' target='_blank' rel='nofollow'>this thread</a>.
First, since not everyone is that into Negima, here's <a href='http://negima.wikia.com/wiki/Pactio' target='_blank' rel='nofollow'>the Negima wiki article on the Pactio</a>.
The short version:
So, in other settings, with other magic systems, the pactio, or an equivalent thereof, would be mechanically different, if it would be possible at all, and would change the setting to varying degrees.
In the Nasuverse, a pactio would probably be a variant on the process of creating a living, human <a href='http://tatari.byethost33.com/fuyuki/magic.htm#Familiars' target='_blank' rel='nofollow'>familiar</a>, and might involve opening any magic circuits the Minister/Ministra has. Given the nature of Nasuverse magic, it might not be all that widespread, unless it has some means of bypassing the 'peak magic' limits, or there's a good chance of getting an Ala Alba level partner out of it.
Let's say its something Zelretch came up with, derived from the Kaleidostick. The circle and ceremony connect you to the Mystic Code that creates the pactios (and paired Mystic Codes in the form of the pactio cards), which draws power from other worlds, thus bypassing the peak mana problem, and explaining why magi are so inclined to use it, despite the drawbacks: it was created after Zel read the Negima manga (first published in 2003, so, just before the Fifth Holy Grail War), and the Mystic Code has both a sense of humour, and a strong belief in the Powers of Love and Friendship. Thus, if you don't care about your partner, you really don't get much more prana out of it than you put in, and if you do care, you get rather a lot. Likewise, the strength of you belief in the Power of Love and the Power of Friendship could grant a bonus or penalty. Also, the decision of who is the Magister/Magistra, and who the Minister/Ministra, is up to the MC, which I'm thinking of calling <a href='http://negima.wikia.com/wiki/Chamo' target='_blank' rel='nofollow'>Chamo</a>. Shirou has a Reality Marble, and thus is usually the Magister despite his few and low quality magic circuits, unless he makes a pactio with someone who also has a RM and is more powerful (Sacchin could go either way, in that case, considering the WTF?! levels of both their situations), has a Marble Phantasm, or possess True Magic. This is especially ironic because Shirou is much more of a front-line fighter than some of his potential Ministrae are.
Most likely, Shirou's Ministrae would have Artifacts, which would be swords (or other items compatable with Unlimited Blade Works) from other worlds, that are especially fitting for them. In general, Artifacts tend to be either copied or summoned from their dimentions of origin, hence being fairly rare. If/when Shirou pactios with Saber (which may require Rin teaching him how), she would at least get a copy of Avalon (after all, its right there, so Chamo doesn't need to go hunting for it), and might also get one of more of the other significant items she owned in life, that she didn't have on her when summoned.
When the Magister/a and Minister/a care about each other to different degrees, and have differing levels of belief in the Powers, the one with more prana can still transfer it to the one with less, but that can lead to the Minister being able to control the flow of prana to the Magister, instead of the other way around (even though the Magister/a can activate or cancel the Minister/a's use of the card, s/he can only control the flow of prana if s/he is the one with more of it; water flows downhill). If Sakura made a pactio with Shinji, they'd be a fairly typical Magistra and Minister, powerwise: Shinji gets nothing she doesn't give him, because she cares about him, but he cares nothing for her. However, he'd be a pretty crappy Minister, all told, thanks to his personality. If Rin made a contract with Kotomine, neither would get much out of it, as they really don't care for each other, or believe in those Powers (well, Rin sort of does, a little, but she's tried to kill that part of her self).
Pactio pairs/groups where each cares about the other work out much better, of course. Shirou, Rin, and Saber from something like the UBW Good End would be bloody terrifying as a Magister and Ministrae. Shirou, Sakura, and Rider from something like the HF True End, even more so, thanks to the prana boost Sakura has in that route. Likewise, Bazett and Lancer would be a hell of a pair, and might be able to avoid getting pwn'd by Kotomine (really, pactioing with your Servant is just good sense). So, there is now a clear and somewhat quantifiable benefit to a magus being a nice person.
Let me repeat that: There is now a clear and somewhat quantifiable benefit to a magus being a nice person.
That could change magi culture quite a bit, no?
First, since not everyone is that into Negima, here's <a href='http://negima.wikia.com/wiki/Pactio' target='_blank' rel='nofollow'>the Negima wiki article on the Pactio</a>.
The short version:
Pactio is a magical contract used by many mages in Negima. The word is based on the Latin word "pactio", the action of making a "pactum" or "agreement". The word 'pactio' is also fairly often called a "provisional contract." Pactios can be created with any magic user, although not all magic users can create a magica circle. The partner with whom the pactio is formed attain abilities related to their personalities. In the remake series, <a href='http://negima.wikia.com/wiki/Negima!%3F' target='_blank' rel='nofollow'>Negima!?</a>, the formation is known as a "neo-pactio."
In the Nasuverse, a pactio would probably be a variant on the process of creating a living, human <a href='http://tatari.byethost33.com/fuyuki/magic.htm#Familiars' target='_blank' rel='nofollow'>familiar</a>, and might involve opening any magic circuits the Minister/Ministra has. Given the nature of Nasuverse magic, it might not be all that widespread, unless it has some means of bypassing the 'peak magic' limits, or there's a good chance of getting an Ala Alba level partner out of it.
Let's say its something Zelretch came up with, derived from the Kaleidostick. The circle and ceremony connect you to the Mystic Code that creates the pactios (and paired Mystic Codes in the form of the pactio cards), which draws power from other worlds, thus bypassing the peak mana problem, and explaining why magi are so inclined to use it, despite the drawbacks: it was created after Zel read the Negima manga (first published in 2003, so, just before the Fifth Holy Grail War), and the Mystic Code has both a sense of humour, and a strong belief in the Powers of Love and Friendship. Thus, if you don't care about your partner, you really don't get much more prana out of it than you put in, and if you do care, you get rather a lot. Likewise, the strength of you belief in the Power of Love and the Power of Friendship could grant a bonus or penalty. Also, the decision of who is the Magister/Magistra, and who the Minister/Ministra, is up to the MC, which I'm thinking of calling <a href='http://negima.wikia.com/wiki/Chamo' target='_blank' rel='nofollow'>Chamo</a>. Shirou has a Reality Marble, and thus is usually the Magister despite his few and low quality magic circuits, unless he makes a pactio with someone who also has a RM and is more powerful (Sacchin could go either way, in that case, considering the WTF?! levels of both their situations), has a Marble Phantasm, or possess True Magic. This is especially ironic because Shirou is much more of a front-line fighter than some of his potential Ministrae are.
Most likely, Shirou's Ministrae would have Artifacts, which would be swords (or other items compatable with Unlimited Blade Works) from other worlds, that are especially fitting for them. In general, Artifacts tend to be either copied or summoned from their dimentions of origin, hence being fairly rare. If/when Shirou pactios with Saber (which may require Rin teaching him how), she would at least get a copy of Avalon (after all, its right there, so Chamo doesn't need to go hunting for it), and might also get one of more of the other significant items she owned in life, that she didn't have on her when summoned.
When the Magister/a and Minister/a care about each other to different degrees, and have differing levels of belief in the Powers, the one with more prana can still transfer it to the one with less, but that can lead to the Minister being able to control the flow of prana to the Magister, instead of the other way around (even though the Magister/a can activate or cancel the Minister/a's use of the card, s/he can only control the flow of prana if s/he is the one with more of it; water flows downhill). If Sakura made a pactio with Shinji, they'd be a fairly typical Magistra and Minister, powerwise: Shinji gets nothing she doesn't give him, because she cares about him, but he cares nothing for her. However, he'd be a pretty crappy Minister, all told, thanks to his personality. If Rin made a contract with Kotomine, neither would get much out of it, as they really don't care for each other, or believe in those Powers (well, Rin sort of does, a little, but she's tried to kill that part of her self).
Pactio pairs/groups where each cares about the other work out much better, of course. Shirou, Rin, and Saber from something like the UBW Good End would be bloody terrifying as a Magister and Ministrae. Shirou, Sakura, and Rider from something like the HF True End, even more so, thanks to the prana boost Sakura has in that route. Likewise, Bazett and Lancer would be a hell of a pair, and might be able to avoid getting pwn'd by Kotomine (really, pactioing with your Servant is just good sense). So, there is now a clear and somewhat quantifiable benefit to a magus being a nice person.
Let me repeat that: There is now a clear and somewhat quantifiable benefit to a magus being a nice person.
That could change magi culture quite a bit, no?