This rule isn't just limited to just big-breasted girls in Negima, as Nodoka, who is a bit of a Pettanko, is seen hiding one of the smaller versions of her Pactio item in her cleavage in chapter 280.
During the sports festival, several girls in class 3-A pull love notes to Negi out of their clevage because they're unable to express their feelings aloud.
Villain Ball: Cosmo Entelecheia attacking the Governor's reception for no explained reason, while they already had all they needed and were supposed to be lying low.
Villainous Rescue: Evangeline saves the gang's collective ass in Kyoto, demonstrating her true power in the process by curb-stomping both a recently-summoned demon god and a later arc's Big Bad in quick succession.
Also often played for laughs when Yue is in a pinch, showcasing her tendency to overanalyze everything.
Waterfall Shower: Done on several occasions, most notably during the descent into the Library in volume 3, and then again much later in the Magical World by Asuna and Setsuna. and the Crowning Moment of Funny when Rakan and Chisame catch each other doing it.
The Watson: Usually the normal or inexperienced girls. The trained warriors are usually the ones explaining.
Well-Intentioned Extremist: Chao, Fate, and Kurt Godel all want to "save the world" through means that others think are going too far.
We Will Not Use Photoshock In The Future: Kosmo Entelekheia edits video of the fight at the Gateport to make it look like Negi's group had destroyed it instead of themselves, causing Negi's group to become wanted criminals. Although it probably doesn't help that there's a Government Conspiracy against them.
Chisamelampshades this early on, when Negi notices how much better she looks in her idol pictures but doesn't put two and two together.
And then, it's all undone by revealing that it's not, in fact, Zazie, but her older sister.
(Then again, there's a lot of misleading foreshadowing in that collage, starting with the fact that the size of most of the characters' pictures is inversely proportional to their later role in the story.)
Chapter 311 Quartum rips Chachamaru in half, Quintum steals back the Code of the Lifemaker, so now there are 4 averruncus' one of which is female.
Chapter 331 features the arrival of all the former Ala Rubra members currently accounted for including none other than JACK Freaking RAKAN to join Eva in taking on KE, giving the impression that Akamatsu is out to either give his readers a concussion or just straight out split their skulls open.
Chapter 334 which ends up revealing the current Lifemaker to be Nagi.
Chapter 346 in which Negi reveals that he has feelings for one of the girls (doesn't so which one though)
Chapter 352 alone blows them all out of the water. Asuna wakes up in the future several years late and meets the descendants of several classmates. Furthermore, she finds Negi's grave (his actual fate remains unknown, however, as an article she read says he disappeared).
The whereabouts and activities of Graf Herman remain unclear, even though he survived his battle with Negi and promised that they would meet again. He suggested that he may know how to reverse the petrification cast on the inhabitants of Negi's village when he attacked it some time before the main story begins, but by the "Where Are They Now?" Epilogue, Konoka went ahead and cured them anyway and he vanishes completely.
Negi's mother, Queen Arika, despite being incredible important and surviving the events that destroyed her country, is never mentioned again. Her reasons for abandoning Negi, or her inability to help, for the less cynical, are never revealed.
What Measure Is a Non-Human?: Negi and Team Good fall squarely on the side of "has a mind, is a person". Kurt Godel seems to think only the human inhabitants of the Magical World are worth anything. Since it's been shown that only humans can survive the Lifemaker's "Rewrite" (meaning that the Rubber-Forehead Aliens and Half Human Hybrids might be magical constructs) he has a reason. Not a valid one (they're still sentient, intelligent beings), but a reason nonetheless.
What the Hell, Hero?: Not quite so serious one in chapter 349: Yotsuba calls out the girls for trying to force Negi to say who he likes, if anyone in particular. Her rationale? He's only ten, they already know about his magic and parentage, several of them have pactios with him and he's trying to save the world. Is he really not allowed to have any secrets at all?
When All You Have Is a Hammer: Negi has a tendency to solve his problems with kissing; such as creating a soul for Chachamaru, and unmasking Fake!Asuna with a pactio.
Negi has apparently rescued his father and defeated the Lifemaker.
Kazumi became a photojournalist through the period of upheaval caused by the Mars terraforming plan, with Sayo still by her side long after she was formally released by Mahora.
Yuuna follows her late mother's footsteps as an agent of Megalomesembria, apparently with Takane and Mei in tow.
Nodoka and Yue started working at the ISSDA; on occasion the former goes out to help her old archaeological comrades.
Haruna migrates to Megalomesembria where she became a bestselling author, with Chamo at her side.
Konoka went on to cure the petrified denizens of Negi's hometown, while Setsuna became a pioneer space traveler with a high-speed cruiser she bought for the two of them, while occasionally still clashing swords with Tsukuyomi. They are also strongly implied to have married.
Ku Fei set up a martial arts dojo at Mahora, and has since continued her winning streak at the Mahora Budokai. Kaede, her training partner, became a wandering space ninja.
Makie became the physical education teacher at Mahora boys' junior high.
Akira became an orbital elevator stewardess, while Ako was healed of her scar and has become a first-grade medic at Mars, while still secretly looking up to Konoka as her inspiration.
Fuuka and Fumika met two princes disguised as animals one Christmas. Their relationships deepen while accompanying Negi, and soon the two pairs got married and were blessed with two daughters.
Satsuki continued her culinary studies in China and France before reopening Chao Bao Zi, which went on to become the first interstellar restaurant chain, while her friends still visit the streetcar restaurant where it all started.
Misora became a guardian of Mahora, with Cocone still by her side.
Chisame seemingly became a full-time hikikomori, but she has since become a special advisor to the ISSDA.
Satomi's theory of integration of science and magic became crucial in terraforming Mars and creating the orbital elevator, and has since married a governor, while Chachamaru worked for many years as Negi's secretary and became the prototype for all androids needed to perform the harsh task of developing the solar system.
Mana has become a wandering gunner quelling conflict wherever she goes, never losing her faith on Negi's goal, and was said to have fought in a 22nd-century revolution which caused Asuna to oversleep for 30 more years.
Evangeline was finally freed from Mahora after Nagi's rescue, although she remains in touch with Negi.
Zazie rejoins Poyo, and has since become a goodwill ambassador from their realm.
Misa has become a station hotel concierge, Madoka became an elevator customs official (while still pining for anyone black-haired and dog-eared, a remnant of her past affection for Kotaro), and Sakurako uses her keen intuition at work at a securities firm.
Chizuru became a proxy representative at Naba Industries, working together with Ayaka to help realize Negi's dream. Once their mission is done, she settles down as a nursery teacher, where she took a liking to the Narutakis' daughters.
Kotaro ran off for some training, with Natsumi quickly following him (under the pretense of a graduation trip), and after years of sexual tension, they finally got married in 2015.
Asuna becomes a living symbol of harmony between Earth and Mars, and has since worked to restore Ostia to its former glory (and presumably resuming her post as its legitimate queen), while Ayaka joined her side after completing Project Blue Mars with Chizuru's cooperation.
Finally, Chao still desires peace for her own timeline in her own way.
Takane, the girl with the shadow puppets. She's supposed to be at least reasonably competent, but has a tendency to go up against stronger enemies (that is, Negi and friends), get her ass handed to her, and have all her clothes blown off.
Any dragons that appear are likely going to be defeated in a spectacular manner.
Essentially any character that isn't Evangeline, a member of Ala Rubra, Cosmo Entelecheia or Negi is pretty much 99% guaranteed to suffer this at some-point in the story.
Also, the series' seemingly abrupt ending could be attributed to this, as Akamatsu ended the series early in protest to a proposed Japanese law giving publishers greater control and ownership over writers' work. This would also be a guarantee that he keeps the rights to his own work if the law passes.
In the situation of Negi and Jack Rakan, whenever they break a seeming rule, it is brought to our attention, such as Chisame calling Rakan the man with infinite cheats, the one time he doesn't break a rule.
Wuxia: Euro-centric magic and fantastic setting aside, the manga is increasingly gravitating towards this genre. Ku Fei's, and therefore by extension Negi's fighting style is emblematic of those found in the Classic Shaw Brothers Kung Fu films and Jet Li films of the 1990s.
Xanatos Gambit / Crazy-Prepared: If the fandom's theories are correct, Chao Lingshendefines this trope. Basically, she's trying to avert some disaster in the future. The best way to do this is to reveal magic to the world. But if Negi is able to stop her, then that means he will also be able to avert the future disaster... well done, my dear. Well done.
It goes even further. Turns out that the entire "Martian Invasion" event was meant to simulate the Cosmo Entelechia attack on the World Tree and prepare the school for it. Dear gods girl.
Note that there is no proof for any of this.
Year Inside, Hour Outside: Eva's "resort-in-a-bottle" (24:1 ratio), Theodora's similar training ground (10:1), and Eva's scroll (max of 72:1, though it can only be used for mental training, not physical).
Yin-Yang Bomb: Kanka is what you get when you combine the opposites that are Ki and Magical power. It is powerful enough to be considered a power category of its own, but is only used by a select few. Takamichi is the most known user and uses it since he is unable to use magic on its own.
Magia Erebea also counts, given that Negi uses the darkest of magic with the light based lightning spells he's most proficient at.
Magia Erebea itself is not dark, and lightning spells are just lightning spells. Magia Erebea is 'dark' because of how badly it screws around with the person using it. Magia Erebea actually counts for Yin-Yang Bomb out of technicality, but would really be better called an 'Everything Bomb'. Which is how it works: Magia Erebea accepts all facets of magic equally, light and dark.
You Are Not Alone: The last two episodes of Negima! (the first anime) revolve around this on multiple levels.
You Can Leave Your Hat On: During the School trip, The magical decoys that Negi's team-members make go haywire and put on a striptease for the class (off-screen). It being an all-girl school, It didn't cause much them much trouble.
You Can't Fight Fate: Both straight and subverted, for the same event. Not to be confused with the character named Fate, although fights against him have been unwinnable more often than not.
Jack Rakan vs Fate played this straight as can be. He stood 0% chance of winning, but was so badass in his refusal to go down quietly into the night that he even made Fate question his motives. And he ultimately subverts it. Even after being rewritten out of reality (twice) he proves that Fate can be fought.
Younger Than They Look: Most of the girls. Lampshaded when two of them try to get discount tickets to a movie, but the ticket saleslady refuses to believe that they're middle school students.
Later, Mana gets a hold of a de-aging candy and is able to buy an elementary student ticket. After having a big laugh about beating the system, she realizes that, with the cost of the candy, she actually lost money overall, making it something of a Pyrrhic victory. Then Kaede shows up in a child's body, but tells Mana that it's due to one of her ninjutsu techniques, so it's free.