Continuing from Origami's appearance in her Inverse form she proceeds to completely DEMOLISH the city. Mindlessly unleashing attack after attack aiming at everything around her.
The plan is to get Shido close to her - the person most precious to her would SURELY be able to bring her back to her senses, right?
Yeah... It didn't go well.
By now Origami is completely unresponsive and according to the leading expert in the field (Kurumi) beyond saving right now.
"Right now" being the important part.
Even not knowing what caused the inversion the plan is obvious - send Shido back 5 years to try to prevent it.
The resulting time loop plot is so complex that it'd warrant 3 post on it's own so I'll skip all of it to say that after a couple of failures Shido's last resort is to push Origami's parents out of harm's way and perish in their place.
But - for those who don't know - death is cheap for Shido who wakes up back in the present.
The city is not destroyed, everyone is okay and nobody at school knows who Origami is since she never moved back from wherever she lived prior to the series start.
Except... There's a new, dangerous Spirit on the loose with her powers not sealed: Devil.
A mysterious Spirit who only appears to attack other Spirits.
And right on cue there's a new transfer student the very next day:
The new Origami is a soft spoken, kind and kinda shy girl who quickly identifies Shido as a "relative" of a hero who saved her parents 5 years ago and died in the process due to looking very much like him.
However. It seems like Death doesn't like to be cheated and Origami's parents still died just a year later leading to her joining the military as before - the timeline did fix itself to a degree. However now Origami didn't do it seeking revenge but rather in order to protect others.
There's still one issue however. If new Origami is like this then can she also be an Inverted Spirit who mercilessly hunts other Spirits?
Well. There's someone who quickly offers help in discovering that.
Kurumi is the one other person to remember everything but even she is not aware of what transpired. It'd take a shot from one of her bullets (Yud) to reveal target's past.
Origami appears on the scene and quickly obliterates Kurumi before coming back to her senses as if nothing - remaining completely unaware of what she just did.
Well. They have their confirmation but forget getting close enough to shoot her with Yud.
Shido resorts to... Just consulting his allies and reveals that he changed the past.
They conclude that since Origami also went to the past her old self returned as well and developed into a split personality when new Origami became a spirit - while also inverting on the spot.