Devil Sync (鬼化内 (シンク・デビル), Debiru Shinku lit. Turn into the Devil Within), short for Devil Synchronization (悪鬼同期, Akki Dōki), is an advanced Devil Slayer ability that is akin to Dragon Force. It can only be used by Leon Fullbuster.
Devil Synchronization is the strongest ability that a Ice Dragon Slayer user can attain within their lifetime; granting the user power that is comparable to an actual demon while at the same time gaining the ability to exorcise and purify all that have a demonic factor within them. While accessing this form, Devil Slayer are referred to as a Cambion (半鬼 (キャンビーオン), Marian lit. Half-Demon) for they are no longer consider normal and, instead, are viewed as the fusion between an Etherious and whatever race they so happen to be.
Devil Sync acts as a stimulant to the body and through it flows much like adrenaline would heightening the users abilities to levels that would allow them to touch the power of Etherious in their respective styles. Devil Sync increases the damage done by standard Devil Slayer spells immensely and grants the user access to more advanced attacks. Intensifying the user's physical prowess in every category and considerably boosting their magic power, even heightening their reaction time and reflexes. When exuded at its fullest, the Magic becomes far more demonic in nature surpassing the previous limitation that would have resided on their magic prior to learning the form. This is often considered the price as for more power gained more humanity is lost.
Because the power within the particles now flows through the body in place of the magic rather being carried within the magic, these particles in exchange for this surging power quickly speed up the process of demonification. The user begins to fully exhibit traits of their gradual loss of humanity within the transformation and find it increasingly difficulty in changing back to their natural human form. The greater the power drawn on within the particles the faster the demonification process proceeds.
When utilizing this form not only does their power increase dramatically, but the potency of their spells, speed, durability and magic energy does as well. Being that their focus is now using the particles their attacks become extremely lethal to mages who are not adjusted to the particles within their body. Poisoning and weakening their magic over the course of the fight. Prolonged battles versus this form can result in heavy exposure and possibly death for the target.