The reader is from our world, he gets sucked through a vortex and into a space where hes merged with the remains of Evolt. He then is drawn into another vortex which causes a Spacial Quake that brings him into the Date A Live universe. Hes brought there a week before official series starts. He is soon confronted by the AST, and he learns to use the Evol Driver. He fights back. Later he finds that the Pandora Box is inside him with all the full bottles and other types of bottles (fullfull bottle, rabbittank sparkling can etc). Also, theres a side effect from the merged Reader and evolt going through the dimension where the spirits are stored, a new being created from the energy and DNA of the spirits, humans and blood species, Pandora Ghouls(I suggest having a single Pandora Ghoul based on each rider in build, except Evol, as well as the hard smash), spirit like beings that appear without the need of a Spacial quake, and are based off of the forms of the kamen rider build series. And when they're sealed, they have their powers dissolve and reform into a new fullbottle.

Here are some fanforms