The supernatural phenomena of Magic ability was first introduced in the original Guilty Gear video game as the source of the combatants' manifested powers and the abnormalities that existed within their world. While Magic is publicized as a scientific study that has advanced the progression of life on Earth, it is also the primary cause of constant turmoil within the world.
Chronologically, Magic was first introduced to mankind by the Apostles in the year 1999 to counter the Dawn of Revival and lessen their reliance on modern technology; contraband hardware that would later be dubbed Black Tech. Prior to the Xrd series, Magic was ambiguously stated to be an unlimited source of energy humans discovered that would be utilized to end world crisis and eventually give way to the Gear Project, that by proxy, spawned a number of other projects including the creation of the OutRage and the Forbidden Beasts throughout the events of the Holy War.
It should be noted that prior to Magic replacing technology and the modern means of science -- general knowledge and understanding that would later collectively be grounded in a field of study known as the Magical Theory of Science, numerous events involving Magic-related phenomena had already occurred within the central Guilty Gear timeline: the existence of immortals, Youkai, Raven's "first death", and Axl stopping gang violence in London and subsequently slipping through time.
Capabilities of Magic
After thwarting the Dawn of Revival, mankind learned to harness Magic into an endless source of renewable energy that solved world issues of limited energy fuel, and with over 100 years of war since its introduction to the human race, Magic and its users have continued to make breakthroughs in its applications and usage. Following the abandonment of modern technology and the events of the Crusades, government military forces and organizations spread throughout the world employ Magic in their arsenals. While there exists technology to produce magical phenomena, individuals are capable of using it themselves (as exhibited by the central cast of the Guilty Gear games).
Magic is adaptive - changing to the needs of the users over a course of time. Products of Magic, such as the OutRage and the Forbidden Beasts, commonly change throughout their subsequent appearances as a result of evolution. Notably in Guilty Gear Xrd, over timeskip: Eddie spawned a symbol on his body that was absent in prior game titles, while Jam Kuradoberi's magical Ki energy is shown to now circulate around her body.
Many characters possess the ability to manifest or summon materials and beings related to their magical power. Dizzy's Gear form is equipped with a pair of wings (Necro & Undine) that have consecutive (often opposing) thought, while she can spawn other miniature Gears that fight in her service; Slayer's cape is a sentient portal; Bridget's teddy bear Roger is possessed by a ghost; and I-No's clothing is shown to have a level of sentience.
The Magical Theory of Science recognizes five components of Magic: Fire, Lightning, Wind, Water, & Ki. However, there also exists the additional element of Light (known only to be manifested through the OutRage Flashing Tooth), as well as Magic phenomena that does not fall into specific branch categories; including time-travel, space manipulation, summoning lesser beings, materializing objects, and so forth. Generally, Magic users adhere a singular component of Magic, and it is unknown if specific elemental components directly counter or offset others.
Fire: The destructive power of flames are a commonly used phenomena throughout the Guilty Gear series. Numerous characters have the power to manifest Fire, conclusively implying that it is perhaps the most common or easiest component to manifest out of the others -- easily augmented into a range of versatile fighting styles in various ways. The OutRage Fireseal and its evolutionary stages of the Junkyard Dog naturally channel Fire-related Magic and amplifies the user's magic ability.
Lightning: Said to be the most difficult elemental component to master, Lightning yields destructive potency that heavily rivals Fire-type spells. Very little is known about Lightning, other than that Ky Kiske himself has notable proficiency in it without the use of magic amplification devices (i.e. the Outrage), in addition to being the elemental configuration of his signature weapon, the Thunderseal. Like Fire, various techniques and spells are shown to produce the aesthetics of Lightning-type Magic.
Wind: Very little information is given about Wind-type Magic, except that Anji Mito wields the OutRage Zessen which channels and greatly amplifies the phenomena. Like previously listed element configurations, numerous spells produce and emulate the effects of Wind. The ability to levitate and fly could be linked to this power, although this unspecified.
Water: Like Wind, Water has a limited number of known users. May's summoning of dolphins (hinted by the present water effects) could imply her use of Water-type Magic, although this is unconfirmed. There have not been any confirmed users of Water.
Light: Channeled and amplified through the OutRage Flashing Tooth, although for unknown reasons, it is not a part of the five elemental configurations.
Ki: In-universe, the least understood of all elemental components, Ki is a metaphysical life-force energy concept heavily linked to the Eastern people and the masters of their ancient fighting arts (Kliff Undersn, Chipp Zanuff, and Venom). It is generally characterized as raw energy, rather than an actual element. Throughout the Guilty Gear games, the Post-War Administration Bureau expresses interest in obtaining and further studying the power, implying that Ki generally cannot be achieved by the Magical Theory of Science. However, every living being within the Guilty Gear universe passively possesses Ki, as shown throughout the events of Xrd, Ki-users exhibit the ability to sense irregularities in Ki and can even manipulate the flow of Ki within another person or object. Ki appears to emulate the effects of other elements, particularly Fire, Lightning, & Wind.
In the "Guilty Gear Xtra" manga, Mizuha is depicted as a Ki user that employed her Magic power in unique, considerably passive ways not shown in the central Guilty Gear story. In addition to possessing a degree of superhuman strength, Mizuha could amplify Magic ability in others and possessed an innate "sixth sense". Furthermore, Mizuha could take on an energized form to teleport and enter a person's subconsciousness.
Kliff Undersn's unique ability to briefly revert to his younger self may be linked to his only shown power: Ki.
Many characters, both playable or not, possess the ability to use Magic phenomena.