Kesseijutsu

Kesseijutsu (結成術, "Formation Arts") is an advanced battle technique designed by Seireitou Kawahiru. It revolves around the same principles that are featured in the use of the and  release states, therefore only Shinigami whom have achieved some basic level of communication with their. The Kesseijutsu is a technique founded in teachings.

Overview
When a Shinigami and their Zanpakutō establish a dialect, they enter into a union between souls. The two souls essentially resonate with one another and allow an even greater power to take form, resulting in the Shikai and Bankai forms. This can only take place between a sword and its master that have come to accept one another on some kind of fundamental level, which causes their souls to somewhat spark a connection and results in a resonance. However, the powers that are generated from this union matter greatly upon the two souls in question. There exists a similar situation in regards to Hollowfication.

In order to combat the impending L'Obscurité threat, Seireitou came to the conclusion that only the Captains and a handful of Lieutenants would manage to carry the fight by their own merits. Lower-class Shinigami would require an alternative means of facing a threat that would normally overpower them in a one-on-one confrontation. Thus, the Kesseijutsu technique was created. The Kesseijutsu allows for a team of Shinigami (and possibly other beings that can communicate with an inner soul) to essentially form a spiritual link between their souls, causing them all to become heightened in power, strength, speed, and other associated aspects by a respective amount. Additionally, their mind and instincts are also linked together, making it possible to coordinate team assaults to an almost perfect and flawless standard. It makes it so those using the Kesseijutsu can even combine their attacks down to the reishi level, creating amazing new techniques that carries much more effect that either of the individual techniques alone. With such an ability, it becomes possible for a group of seemingly weak Shinigami to fend off a single powerful Captain-class or stronger foe with ease. When in use, it is signified by a spark of white reiryoku discharge that snaps between the teammates, following by their eyes all glowing with a faint hue of white spiritual energy for a brief moment.

However, despite its vast benefits, the Kesseijutsu requires immense practice to perfect. Those involved in the team must be able to communicate souls together and not attempt to impose their will over another. At all times, they must maintain a balanced level between their souls, or else the Kesseijutsu shatters and falls apart. In addition, the concentration and practice required to preform the technique is proportional to the amount of spiritual power that each user possesses individually, the differences between their personality and mannerisms, and also in regards to the number of teammates preforming the Kesseijutsu; with greater numbers requiring an even greater level of concentration. Despite this, Seireitou has declared that the Kesseijutsu has no limit in potential, meaning that it is theoretically possible for an almost indefinite number of fighters to use it at a single time. It seems that another factor involves whether or not the Shinigami are utilizing their Zanpakutō's release states, which actually equates to an additional user entering the formation and thus a greater effort is needed to execute the Kesseijutsu properly.

Variations

 * Kamiriki Kesseijutsu (神力結成術, literally "God Power Formation Arts"): Essentially a variation of the original Kesseijutsu carried out by a team of superior warriors of individually immense power. The only known use of this has been demonstrated by Seireitou and Raian Getsueikirite, which was done just once to fend off Kurama Kawahiru.

Behind the Scenes
This is a concept inspired by the Chain Resonance found in the manga and anime series, Soul Eater.