Since quite a few years back, it's been quite commonplace in fantasy anime and manga to represent casting magic as some kinds of 2D circles or geometric figures with patterns, possibly multiple ones, as in the image on the right (Frieren). I see this idea used in almost all – if not all – anime and manga now.
It hasn't always been that way though. Older anime and manga used other and different kinds of representations, say from blinking stars (image on the left, Majokko Megu-chan) to smoke, or even just sound effects.
I'm just curious: does anyone have any info or links to share about how this "2D representation" came about and why it's become so popular? Cheers!
Okay, so magic geometry, circles and runes have a long tradition in the West, for example in what is commonly called hermetic magic (think alchemy, circles, pentagrams, etc.)
From this we get the tropes of Geometric Magic and that evolved into Instant Runes.
In regards to chronology:
Anime and Manga has increasingly relied on western magical themes as it found new audiences in the west and also because hermetic magic is as exotic to east Asians as shamanic magic is to Westerners.
But more importantly, as the medium moved into mass production and pop-culture, the budgeting for especially anime (who used to be way more handcrafted) became tighter in regards of time and money. Animation studios looked for easy ways to animate, The best example of this is the mouth on the cheeks (because for talking, they only had to redraw the mouth, not the entire head of a character) but also many character-details and very intricate magics had to be replaced with something that was more animation-friendly.
Now, magic circles are REALLY easy and quick to animate, while also looking really intricate and complicated at the same time. It's an easy way to "suggest" detailed and intricate effects without using up your animation-budget for things that are not as relevant.
This is why the industry started to increasingly use "cheap" but good looking animation-techniques like magic circles. Games picked it up from there because it was a useful tool to show area of effect for spells and later this became a case of cross-pollination as anime in turn started to become more computer animated and lean more on game graphics, that had already proven successful in game animations.
So there you go.