Ascension is an incredibly high level skill that is mastered only by a handful number of Exorcits, considered the pinnacle of the Exorcist's techniques. During Ascension the user gains white hair, a spiral sigil on the centre of their forehead and ringed white irises. The technique unifies the minds of user and the Tsukugomami, allowing them to temporarily perform super-human feats, greatly enhancing the combat ability of the Exorcist. For an Exorcist to be able to use Ascension they need not only a high level of mastery and skill, but also a deep bond with their Tsugumomo to reach a state of possession where they're both perfectly synchronized. In order to utilize it is needed for both of them to be in agreement, meaning that the freely use this mode at their own leisure. It is, however, possible to forcibly trigger Ascension by having the owner call their Tsukumogami's true name.
While Ascension is an incredibly powerful ability, the power employed during this mode greatly exhaustes the body of the user. When Ascension finishes, the user is left depleted of their energy and unable to move for an extended period of time, with Kazuya being in this state of exhaustion for 24 hours. Additionally, the Tsugumomo partner becomes unable to use their abilities for that same period of time. The amount of time Ascension remains active depends on the stamina of the user, and will automatically wear off once they reach their limit. This makes of Ascension a last resort trump card, since if they're unable to finish off their opponent before they reach their limit they would be rendered defensless. If Ascension is only activated for a very low period of time, like only a couple of seconds, there are no side-effects.