The physical pseudo-spiritual manifestation of Chinami's absolute obsession with having control over her own life, gained in a moment of despair over being at the mercy of the whims of what she perceived as a "ROB" (Random Omnipotent Being/Bastard)... and the encounter with a dangerous supernatural virus.
At its core, it is a power gained by being infected with strange spiritual virus, a virus which is non-transmissible and can only be contracted by making contact with its pure form. In such a case the subject will die unless they prove to have a certain strength of character, a conviction to bend the world to their own will. It is a virus that at its core, culls anything and anyone it perceives as weak. Upon surviving it, the victim is "rewarded" by the awakening of their Spirit, an often vague manifestation of their innermost self. Once death or "worthiness" has been determined, the virus dissipates from the body, unable to be extracted or otherwise analyzed.
The power typically manifests as a humanoid being that can move a variable distance from the owner and selectively interact with the world... while possessing a personalized power that is typically modeled after some prominent portion of the owner's personality. These "Spirits" cannot be harmed by any force except another Spirit and are typically invisible except to those with high spiritual awareness.
Chinami, in particular, is a person who firmly believes that she will never have to change for the world... and that the world must, instead, be made to change for her. Her power thus manifested as such.
A pearly-white & electric-blue humanoid being of almost robotic appearance decorated with celestial imagery, Living on a Prayer (as Chinami chose to name it) can only move up to 5 meters (about 15 feet) from Chinami in any given direction. It is fast enough that it solidly surpasses lightspeed, but Chinami has no clue exactly how much so. Strength-wise, it is less obnoxiously impressive, but still strong enough to send an Iowa-class battleship tumbling ass over teakettle with a casual shove or to annihilate entire city blocks with a single punch. The Spirit has a reaction speed as ridiculous as its actual speed and greatly heightened versions of the five basic senses.
Chinami is able to simultaneously perceive the world through her own and her Spirit's senses and, thus, is quite difficult to catch off guard. The Spirit can also interact with the world in a selectively tangible way, reaching inside an object/creature and grabbing hold of something. As a result, she can also overlay her Spirit over her own body, physically enhancing herself to levels greatly inferior to the Spirit's true potential; the tradeoff, however, is that she may benefit from the practically conceptual durability of her Spirit in turn, using it as an utterly inviolable armor.
Its primary power, however, is the ability to copy and paste an alternate version of a target object or living being onto the local universe version. The ability essentially browses the multiverse and then imposes a new version upon the target. With this power, Chinami can instantaneously heal and harm, grant new powers to others or wrest what they already have away. It's flexible enough that she can even impose alternate locations on a target, effectively allowing teleportation. Her power will only specifically impose the changes she desires and otherwise defaults to the condition of "otherwise unchanged" on any given target, unless Chinami specifies otherwise.
While she is capable of effecting minds and memories with this ability, it actually happens to be a firm line in the sand that she will absolutely not cross for any reason, considering how sacred she holds free will.
The changes are permanent or temporary at Chinami's discretion.
The main caveat to this ability is that the Spirit must make physical contact with a target they mean to change, and her relatively short range can quickly become an issue, especially if she is currently being forced to shield herself with her Spirit as makeshift armor. The final weakness is that the more esoteric a change -and the further she reaches for an alternate that diverges greatly from the local universe's current version of a target- the less instantaneous her ability can activate. This means that when faced with beings of a cosmic or conceptual nature, she can have incredible difficulty effecting them faster than they can get away... if at all.
In theory, she could use her power on herself to gradually strip away and mitigate all these weaknesses, but Chinami has long held these sorts of "natural" limits to her ability as something she must retain in order to not lose her humanity entirely.