So, Erin and I started a Ouran High School Host Club thread... with magic~! And here's the magic.
The magic has Principles. These Principles can be set to other things via a complex ritual involving a lot of magic and users of all of them. The last time this was successfully accomplished was in the Middle Ages, and the people who set it up set the seven heavenly virtues as the Principles: chastity, charity, humility, kindness, temperance, patience, and diligence. Their opposites, then, are lust, greed, pride, envy, gluttony, wrath, and sloth.
When you act in accordance with the Principles, you start storing harmonic magic. When you act contrary to them (in accordance with their opposites), you gain dissonant magic. It is possible to have stores of both by acting in accordance with some Principles and contrary to others, but if you act in accordance with a Principle and then act against it (or vice-versa) you lose the magic you gained in the first place, so most people have approximately no magic stored, on average. Moreover, even the people that do have magic have a real hard time noticing it. It's like Tom Cruise's middle tooth: most people will never realise he has a middle tooth until they are told, and then they will never be able to fail to notice it, but some people notice the tooth all on their own. It is of course much harder to notice than that, so the vast majority of people just won't notice it. After noticing it, though, you'll be able to direct your actions to be more effective at gathering magic, and you'll be able to know when other places/people are using this magic or have had it used on them.
The stores of magic are fuzzy and not really numeric; they work more like the magic owing you favours than like some quantity you spend to do stuff. If you are very harmonious/dissonant, you can pull off bigger things, and that does deplete some of your magic store but not in an altogether fixed and easily measurable way. If the magic "trusts" you particularly, you can even pull off stuff that's way bigger than what you'd strictly be able to do, but if you do that and then stop acting relevantly harmoniously/dissonantly then magic feels cheated and you'll have a hard time rebuilding your magic later.
The kinds of effects you can achieve are more based on the #aesthetic than a specific list of things. There are some things you can achieve via both harmonious and dissonant magic, and some things only one of those can do. As an example, suppose you have a bouquet of 100 red flowers and 1 blue flower. You can easily use harmonic magic to turn the blue flower red to fit its surroundings, or a bit less easily use harmonic magic to turn the red flowers blue. You can't turn them altogether different colours, though. If you use dissonant magic, however, you can in fact turn the bouquet into a rainbow of colours, or turn them blue-and-red, but you can't ever turn all of them a single colour - although if you're clever you can turn all but one of them blue. The relevant #aesthetic for harmonic magic is enhancement, improvement, equality, coherence, reinforcement, maintenance; the relevant #aesthetic for dissonant magic is change, breakage, chaos, decoherence, contradiction. There is probably something akin to "moving your pain from left to right" associated with using/noticing the magic but Erin and I haven't been able to come up with anything like that yet.
Magic is secret, and it's mostly only the elite of the elite keeping it, the rich and famous who apply it to secure their success. It's easier to apply magic to processes than to end results - in other words, making sure a cake you're baking comes out delicious is easier than getting a cake and then trying to make it tastier - and the families that know of magic often apply it on themselves and their children as they grow up, making it more likely for them to turn out pretty, smart, athletic, sociable, etc. It's also easier to apply magic if you're more specific about what it's affecting and if you know more about your target - a doctor would have an easier time using magic to kill a disease because they can target better, it's easier to do magic to objects than people because objects are simpler, it's easier to do magic to yourself than others because you know yourself better.
~Fin