They were most commonly long pieces of brown or white paper of consistent size and length. The large writing on them was red in color and took up most of the paper.
Defensively they have been used for multiple purposes. Many were placed on the doors to the demon weapon room hidden under Second Shibuya High School to impede the influence of the cursed gear kept within.
They have been used by people such a Sayuri Hanayori as a defensive measure to help diminish the effects of activated cursed gear. In other circumstances she was able to manipulate two at a time to dispel the after effects of a vampire sword attack, with them flashing blue and disappearing with their magic having been used.
They can also be used by medical staff who, in combination with modern technology can reduce the effects, but not cure the apocalypse virus. Here, they functioned as an effective supplement alongside other technological counter measures. Though they are not failsafe, overall they serve as a useful buffer against various magical forces and can lessen their effects.
Mahiru had planted wards all over and seemed sure that they could be used to block Yu and Mika's escape route, yet Guren believed they could get past them.
In his fight to capture Mika and Yu, Guren was able to use a single large spell tag that could both resemble his physical appearance and convince Yu's Asura-kannon, infinite blades, knot of fate power that it was the real Guren for the swords to target and stab accordingly.
Though outclassed by cursed gear and other weaponry, spell tags could still be relied on for unconventional combat styles. Despite their small size, some could generate tremendous destructive power. Guren Ichinose made use of destructive spell tags to catch opponents off guard, more so when they were unsure of their purpose.
The spell tags could automatically attach themselves to the target and through magic would remain there, unable to be pulled off. They could also apparently be detonated at the will of the placer, for instance Guren could cause one to explode during a training session with Yu for a distraction. Similarly the caster may exert some control over the impacts that a spell tag could have, such as the size of the explosion. When practising against Yu, the explosion did little more then produce a minor bang to illustrate that Guren had won the practice round. On the other hand, their possible full power was witnessed when Guren was fighting against Mika. One spell tag had the power to level a multiple story building and cause extensive collateral damage with its explosion.
During the training session, Shinoa recognised what the spell tag was and told Yu she would disenchant it, so their power could be overcome that way. Though their destructive power could be immense, stronger vampires were capable of out speeding the explosion itself. Similarly their explosive effects could be defended against with a sufficiently powerful being with an equally proficient weapon, as Crowley Eusford demonstrated.
Eventually the Hyakuya Sect would also gain possession of the spell tags, using them in similar manners as the JIDA. However they also developed certain techniques shown when they manipulate the spell tags using them on their chests.
Guren used smaller spell tags that were attached Mika and Yu to release an energy to bind them.
Using her cursed gear, Sayuri could produce a sword made from multiple spell tags combined together. These were strong enough to withstand lower ranked vampire weapons, and deal damage to them. Though able to hold its own against lesser vampire weapons, against first class weapons, like Mika's, the magic failed and the sword fell apart into now useless spell tags.
- ↑ Owari no Seraph chapter 87 (p. 8)
- ↑ Owari no Seraph chapter 89 (p. 7-8)
- ↑ Owari no Seraph chapter 89 (p. 9)