Spellblade

"A strike that can be neither dodged nor blocked, thereby guaranteeing death. Fulfill these conditions within the one-step, one-spell distance, and you have what is called a “spellblade”." — Lanoff Evarts, founder of the Lanoff School of Sword Arts.

A Spellblade (魔剣, Maken) is a technique that serves as the ultimate pinnacle a mage can achieve with the Sword Arts.

Information
In the world of Sword Arts, there is a single unspoken goal that all practitioners share and that is to create a Spellblade. According to Lanoff Evarts, a Spellblade is a technique that is executed within the one-step, one-spell distance that will, without fail, kill an opponent. In the history of the Sword Arts, the number of Spellblades have constantly fluctuated but in the past millennium, the number of Spellblades neither increased nor decreased as six Spellblades have remained extant; despite this, most other mages don't acknowledge the existence of the Spellblade as they have never once seen it before and even among practitioners of the Sword Arts, proper knowledge of the Spellblades is quite limited. Not even their names are known to the general populace let alone their abilities and their wielders, however, this would not stop entrepreneuring practitioners from attempting to create a Spellblade themselves to disprove the onslaught of voices that deny the very existence of the Spellblade. As such, many people throughout the ages have tried to create new Spellblades but these efforts have largely failed with simultaneous efforts of similar nature, analyzing the existing Spellblades to record its nature, also seeing similar levels of failure. When two spellblade users face off in earnest, they get an omen-like intuition that they can each use a spellblade before any is actually used. This is called Law of Spellblade Simultaneity (Grand Arts Synchronicity).

The First Spellblade
Nothing is known of the First Spellblade except for the fact that 'it exists '.

The Second Spellblade - Creumbra, the self-racing shadow
Used by Theodore McFarlane. Known as the self-racing shadow, the Spellblade works by moving slightly over 50 percent of the caster’s proportional existence to the far limit of their spatial magic, thus creating a doppelganger, something the world doesn’t allow. Immediately, the world begins to correct the phenomenon and merges the two doubles, converging at the position with the greater proportional existence, being the doppelganger’s position. The resulting force of the correction is normally too much for the body to bear and would kill the caster, creating a massive explosion. However, should the force be contained and focused into an attack, it creates a blow that cannot be withstood, delivered without even a flick of the blade. The attack is so strong, it evaporates the target instead of piercing them.

The Third Spellblade
Nothing is known of the Third Spellblade except for the fact that 'it exists '.

The Fourth Spellblade - Angustavia, the thread that crosses the abyss
Formerly used by Chloe Halford. Currently used by Oliver Horn. Known as the thread that crosses the abyss, this Spellblade functions by envisioning the future as an innumerable number of "threads", one of which are guaranteed to bring the caster to victory. By marking that thread, the caster would draw themselves towards that future. Sequential order is flipped on its head. Instead of building up the present towards that marked future, the caster forcefully brings the future into their present, thus bringing them to their marked victory. Oliver Horn's true spellblade is a variant in which he searches for a "thread" that brings him the most pain instead of victory. Due to the logic that pain can only be experienced when one is alive and one lives only by defeating their foe, this leads to a similar result.

The Fifth Spellblade - Papiliosomnia, the dream of a butterfly that never wakes up again
Used by Demitrio Aristides. This spellblade functions by inducing the target into a state of selflessness, where subject and object are not separated. This blurs the target's cognition, making them lose the ability to distinguish between themself and their opponent; between attacking and being attacked. The caster then guides attack and defense to a result in which only the target is killed, typically by making the target kill themself. Because the target mentally agrees with the result, there is no resistance in the process.

The Sixth Spellblade
Nothing is known of the Sixth Spellblade except for the fact that 'it exists '.

The Seventh Spellblade
While still currently unnamed, Nanao Hibiya was able to unconsciously create a Spellblade in the final moments of her and Oliver's scuffle with fourth-year Vera Miligan. Nanao herself is completely unaware of what exactly she did but as a fellow user of a Spellblade, Oliver was able to completely understand what she had done. Nanao's Spellblade is an attack she subconsciously conceptualized when she needed to overcome the speed of light; it is a spell that cuts everything in front of her, returning all obstacles to ether, slicing through formless space, the passage of time, the concept of distance, and everything else in between.