*
"... Oblivion Magia." (Lastia)
"...!?" (Eterna)
How? How was she able to deploy it immediately? The moment she was revived, the interdimensional bunker was breached. The overflowing energy would have cooked them alive, it was an attack surpassing a sentinel's defensive capability, even if it was just shoddy work mending cracks in the bunker. It was sufficient to push her to A grade, even if her body couldn't contain that quantity of magic she could briefly use it before it leaked out of her body.
"This was taken out of Giselle's book, an Oblivion Magia meticulously designed for {Feed}." (Lastia)
Why was Giselle so easily able to break past her limits? How did she climbed the ranks so quickly, becoming a deity a few months after her birth. Giselle was an envoy of the world tree, from the very start their {Feed} were different skills, but they shared an identical personality so their skill name ended up the same. They were always 2 different individuals that shared an origin... Giselle's {Feed} easily absorbed energy and recycled it with maximum efficiency. Lastia's didn't, and it was a deliberate design that could only be overlooked because Lastia hit her limit and died, while Giselle lived in her place and continued her legend for her.
Giselle was a 'pretender', someone who borrowed the name of another and achieved more than the original, bringing more fame to that borrowed name.
All that fooling around did wonders and deceived the world of the nature of {Feed}. Lastia's {Feed} fed not on energy but on information. As a side effect it also absorbed and reused energy but at a significantly lower efficiency, two layers of inefficiency impeded her, one on Giselle's and another on Lastia's which was a bootleg of Giselle's. That's why...
"I can't stop the deployment. It isn't following the usual rules, it's devouring them..." (Eterna)
"That's right. By it's very nature, {Feed} is gonna ignore your stupid laws and digest it into sludge." (Lastia)
That's the nature of Lastia's {Feed}, the one and only. It absorbs and recycle information, erasing the existence of its prey as a result. Rather than dying, the target is converted into a 'ghost' that cannot interact with reality. Eterna's powers hinged on her absolute dominion over reality.
" How... Where did this differentiation stem from?" (Eterna)
Let's break it down. This 'ressurection' might be a deception against the heavens, the fact that no universal law has been acknowledged as being violated lends some credence to the process that Sariel completed. The real Lastia might be still dead, and this was just a clone that imitated her from the genes, personality, to the magic skill and soul. An imitation with virtually no difference from the genuine article. Who's to say that she wasn't? It was impossible to verify, otherwise there would be no meaning to it all.
"From Giselle's will. That's when we differentiated." (Lastia)
It wasn't Giselle's creation or development of free will. It was when she accepted herself as someone different from Lastia. A pure being like Giselle, a wandering unconscious soul that slipped into Lastia's creation and was developed into a weapon... Yggdrasil couldn't have been created without Giselle, Yggdrasil was the mere vessel for the world tree's envoy to be born. Just like how when humans are born, there was no choice for a new soul's creation or whichever other soul slipped in.
As for Lastia's resurrection, it was undoubtedly Lastia's soul and body standing right here. The soul that departed into the world of the dead upon fighting the Calamity, the body that was decomposed into nutrients when Giselle ascended. It was all the genuine her as far as Lastia was concerned.
"I see, then die." (Eterna)
Invisible to the naked eye, a single cleaving wind strikes at Lastia's brain with enough force to turn it into mush multiple times over. An A grade magical girl can survive a decapitation but not too many times, destroying the mind should be sufficient for this threat. However... Nothing happened. A smooth smile is adorned on Lastia's cheeks, like a crown of gleaming jewels.
"... I've deployed my own Oblivion Magia, since before I went out of the bunker. Over here, information breaks down instantly. As long as you remain within it, {Feed} is having an effect on you." (Lastia)
Reddish black plates slide against on another, materialising into the floating air while causing a ruckus. When Lastia was done, she had greaves and boots of reddish black metal. Their sheen bloom around their lustre, painting dark spots over the surroundings. Lastia's Oblivion Magia isn't enclosed, instead it spreads like paint over a canvas, gradually swallowing the world around them.
Without any pause, Eterna slides to a close distance and swings her arm. Her fingers shaped into a hand knife, piercing the air with an impossible speed matching {Swap}. Lastia weaves her body to the sight, catching that knife hand with her own grasp, the firing an uppercut with the other. In return, Eterna smashes her fist into Lastia's face, sending her body flying.
"You can't absorb me, and certainly not all of my attacks. How do I described what happened before...? Right, a fluke." (Eterna)
"You'll regret that." (Lastia)
Unfortunately Lastia wasn't much different from the other magical girls, perhaps one of the selection factors to awaken the magic gene was to be a meat head. The Lastia here is an imaginary being, someone who already died from the bunker breaching attack. A walking mass of information thriving on {Feed}, a single continuous magic spell, a fictional entity with no bearing on reality other than {Feed}. Like a pile of rocks tied by a single string, she was exceptionally fragile.
Dying and ressurecting again, {Blazing unreality comes for all}, {Endowed truth seeks promised returns}, {Against the looking glass}, {Death blooms in stasis}, {Swap}, a faint miracle of an existence held together by 5 A grade spells. A fairy tale that should not have been will not bend to the universe's laws. Under such conditions, {Feed} evolved the moment she revived. Or rather, instead of evolving it merely shed the facade of this era without her knowledge. The true effects that are evinced, the ostentatious display of will...
"Traces of the mystery era, {Envy}." (Lastia)
The heroine who couldn't have anything due to her curse... Naturally wished to have everything. Those that didn't have the curse, those that lived as they pleased... The culmination of culture of human history in Eterna and the sentinels, the very embodiment of the passage of time endured by the human species... As someone who couldn't exist beyond a single day, as someone who lived and died numerous times at the point of midnight... If she didn't want it all out of spite, would she still be human?