"Magic" (and subsequent adjectives such as magical) is a term utilized in relation to Gem technology and abilities. The existence of magic as a supernatural force within the universe of Steven Universe is the subject of extensive controversy and speculation.
Use and meaning of the term
Pearl uses the word rather liberally in various episodes, particularly in Season 1. She describes the gemstone abilities as "magical" in the very first episode, and uses the term "magical artifacts" in "Serious Steven".
To date, no other character uses the term "magic" or "magical" in relation to Gem abilities or technology, though neither Garnet nor Amethyst dispute Pearl's claims and terminology. It is possible that Pearl, in her attempts to sanitize and glorify Gem history and culture, is using these terms as a way to mystify Gemkind to Steven, or at least oversimplifying what they actually entail. However, given several aspects of the universe's ontology described below, it is also possible that "magic" does in fact exist as an actual supernatural force.
Gem reproduction is apparently reliant on what is termed as "life energy". Injectors function by extracting life energy from their surroundings and infusing it into gems, creating Gems. This suggests that magic is reliant on ambient energy, and that it is a substance present in all beings, organic or otherwise.
Gem beliefs and spirituality are never explored in detail, but there is evidence of organised religion due to the existence of temples as well as a "Moon Goddess". It is unclear which roles these beliefs play in Gem magic, if at all.
As mentioned above, magic is quintessential to Gem technology, and arguably what it is in general. Through it, rather simplistic objects made of stone are made into a variety of utilities such as warp pads, extra dimensional doors and ships. Additionally, magic is also behind the various supernatural abilities Gems possess, such as elemental control or psychic powers.
Onion uses the Replicator Wand, suggesting that some artifacts can grant use of magic to humans. Provided he isn't ultimately Gem-related, Lion is also another organic being with magical abilities, as is Lars, but this is due to Rose Quartz's (and Steven's) intervention. Finally, the Crystal Basilisk seems to be a fully organic being with gemstones grafted into its flesh.
- The ambiguity of mysticism within Steven Universe might be a reference to Clarke's Third Law, which dictates that sufficiently advanced technology is indistinguishable from magic.
- The existence of "life energy" suggests that Vitalism is true in this universe.