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) is a technique that serves as the ultimate pinnacle a mage can achieve with the Sword Arts.

Description
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.

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

The Second Spellblade
Nothing is known of the Second Spellblade except for the fact that ' it exists '. During their visit of Galatea, Oliver Horn and Nanao Hibiya are flagged down by Theodore McFarlane who baits Nanao into fighting a slasher; that duel ended favorably for Nanao, however, she was unable to defeat the slasher. Theodore took on the slasher himself and revealed himself to be the user of the Second Spellblade, which carries the name of Creumbra. Known as the self-racing shadow, the Spellblade works by creating a doppelganger...

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

The Fourth Spellblade
Nothing is known of the Fourth Spellblade except for the fact that ' it exists '. However, this can be relatively disproven as shown when Oliver used the Fourth Spellblade in his duel with Darius Grenville who said that the Spellblade ' should have been lost '. Indeed, the actual wielder of the Fourth Spellblade—given the name of Angustavia—was Oliver's mother, Chloe Halford, however, through an incredibly arduous training method, Oliver is able to temporarily house the soul of his deceased mother and obtain her skills in the Sword Arts, including her Spellblade. Nevertheless, as it is merely a borrowed power, it takes a massive toll on Oliver's person; in fact, according to Oliver himself, if he was to use the Fourth Spellblade three times consecutively, he will kill himself. As per its title as the thread that crosses the abyss, this Spellblade functions by envisioning the future as an innumerable number of "threads" in which one of those threads are guaranteed to have the one-in-ten-thousand sword strike that would kill his opponent. By marking that future, he would draw himself toward that future and with sequential order flipped on its head, the pull of destiny is reversed and the rushing flow of time draws Oliver to the one-in-ten-thousand sword strike.

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

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.