Magic

Magic is a natural force utilized throughout human history. In recent centuries it has been weakening. Earth and the dimension it sits in is a "heat sink" for excess magic. It acts as an escape valve for it. Life and humans evolved on Earth (and other planets in other galaxies) as a result of this prolonged exposure to magic, and humans became a sort of magic themselves. Consciousnesses and sentience are in fact forms of magic.

Artifacts
The specific instruments used for magic have varied throughout history and cultures but in general, the process involves a source, and channel, and a target, or "sink."

In ancient times when magic flow was plentiful and consistent, Sky Country acted as a direct source. In modern times, the flow is significantly lessened, and in order to get to levels high enough to be useful, magic from Sky Country has to be concentrated in deposits of magic-sinking material, organic or inorganic. Collecting magic from natural sources and concentrating it into a usable form is known as refining. The usable form is known as vinaliam. Vinaliam can be stored and tapped into as a source of magic.

Using oneself as a channel is a lost art due to magic technology that makes it easier (and safer) to use a specifically designed channel, like a wand or talismen, to channel magic instead. This has made magic more accessible to the population but is less effective than self-channeling.

Source
Magic is naturally generated from the beings in the other world, that Shida refers to as "Sky Country" because the blue sky is reflected from that world. The amount of magic that flows from Sky Country depends on a lot of different factors, an important one being the activity of the beings there. With the recent conflicts and decreased population, the amount of magic flowing to Earth's world has decreased over the centuries.

Magic permeates everything on earth, especially living things. Because sentience is a form of magic, the more sentient a creature is the more magic it contains, with humans providing the largest amount. Sourcing magic from living things is colloquially termed 'blood magic' and provides the basis of animal and human sacrifice.

Different cultures have different creation myths as to where magic comes from.

Historic examples
Al-Jazari: Ismail Al-Jazaria, and famed magician and inventor in the 12th century. Legend says that he designed an entire palace filled with automatons and other magic conveniences, including indoor plumbing (self-filling basins and baths, self-emptying toilets) and a giant rotating garden.

Bani Musa: Either one magician or two brothers. Magicians and astrologers.

Gardens of Al-Andalus: A Moorish king with a kingdom so skilled in magic that he had an open-air garden with perfectly controlled weather and flowers from all over the world, and some that he created himself.

Iyen-he-a: Present-day Cahokia, whose upper class lived in towers and floating islands and could travel to high vertical distances with magic wings. Their civilization was highly advanced and skilled in magic concerning water, but two rival families ended up destroying the area around it, and the entire city. Their main method of transmitting information was through "water panes" that required a separate device to read. Although some water panes remain and possibly contain a great deal of information, the destruction of the city meant the loss of all the devices and they will remain unknown.

Chalawan's Cave and magic sun

Zhuge Liang calling the wind

Current situation
Magic has faded enough from the world that it is just a curiosity now, limited to minor magic like "house magic" and some larger examples in well-established institutions. Humans have been compensating for the loss of magic over the centuries by developing technology at different rates. In the last few centuries as magic has faded and become less prominent and less reliable, knowledge of magic and those very skilled in it have been lost to the ages.

Some even say that historical examples of magic are merely legends, and that the there are suitable scientific explanations for minor magical phenomena.

Very rare examples of old magic still exist in remote pockets, for example the Bear Grandma witnessed by Joel on the plains.