Tensura x Kumo desu ga, nani ka. Crossover.{COMPLETED}

Prologue

If you've read a few fanfics, you should already be familiar with the writing style, but just in case for those that don't know.

"Hello" <- this is talking
'Narrator'
(Thinking)
[system]
<...> this is Ciel
>...< Rimuru to Ciel
"' telepathy "'
{skill}
*action*
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This story takes place just after the final chapter of 'Kumo desu ga, nani ka' and a few decades after the final chapter of 'that time I got reincarnated as a slime'.
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Shiraori pov:

(It's currently been a day since I've been in this insect cage trying to regain my strength and it's coming back, slowly but surely. I've also been trying to find a way to get stronger quicker.
And I've found it, I finally found it. There is a massive drawback to this though, can you imagine it, I have to ... wait.)

(Yes I quite literally have to wait an entire two months, just to regain my power and then I'm still not nearly strong enough to challenge D.
So in the meantime I'm going to try and search for a way that will allow me to gain a lot of power in a small time frame. I to tell you the truth, it's also a way for me to get rid of the boredom. I have literally nothing else to do but wait and wait, so this is another way for me to keep myself busy with something.
I mean it's the only thing I can and it might benefit me in the future, so i am pretty okay with being locked up here, plus the only person that I see is the maid from yesterday and even she only comes in three times a day to provide me with food.)
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D's pov:

(Im bored, I literally only returned yesterday and I'm already bored, how is this possible?
Oh well at the very least I have some form of entertainment, I mean the camera I put in Shiraori's room is perfectly hidden so she won't find out I've been watching her.
She at the very least entertaining me with her squirming and trying to figure out a way to get out of here.)
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Time skip 3months:

We see a humanoid with: white hair, pale skin, red eyes with 5 pupils in each and a white robe/dress made with a fine {divine thread} sitting down on a couch next to her bed.

"Ah , im so bored, it's been about a month since I regained my full power, but I'm incapable of even exiting this damn room."

Shiraori's pov:

(Now that I've regained my power I've tried to several things to increase my power by a lot, but so far I've found nothing and even though my power is still growing at an exceptionally fast pace, it's still not even close to D.)

(Oh ,thats it, I think I found a way to increase my power even faster)
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5 Years time skip:

We see two figures standing on the surface of moon, one was a girl with black hair and brown grayish eyes (I know she had black eyes, but just go with it.)with the school uniform from years before.

And on the other side we see a white figure with scythe in her hand.

A stare down took place with the two figures simply staring at each other, simply waiting for the other to make a move. The first one to move was the white figure that had a glint in her eye screaming 'finally'. The next few seconds there were thousand of clashes happening around, with one clash even causing a shockwave that destroyed the surface around them for miles on end. They were moving around at a speed that most couldn't even comprehend and yet the two figures didn't have any problems whatsoever to keep up with each other even going as far as to say the other looked quite slow, but that was natural, after all these two beings use their magic to accelerate their mind and thoughts, there is one fatal problem about this technique and that is their minds were faster than their body's        Because of this if they move a little to late they would get hit and that is exactly what happened. A few minutes had past and the moon they were on was no longer. They had destroyed it with their numerous clashes and magic spells, the two figures were standing still in the middle of space with one of them breathing a bit faster than the other, this was because she was hit and had a huge wound that was regenerating at an slow speed which surprised her considering that she had an incredibly fast regeneration ability, yet this wound was going so slow she had no other choice but to forfeit, since she didn't want to die and neither did regeneration magic work as that is the case she forfeit.
The other figure had a look shock as she never expected the other figure to forfeit because of this wound, she was both happy she was finally free, yet dissatisfied with the battle and at last she accepted and went back to earth together with the other figure.
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Shiraori pov:

(I'm kinda disappointed, i mean I am finally free but the fight for it was to easy, it didn't even last as long as I expected and what disappointed me the most was that she gave up. I mean I get it, she still has a lot of work to do and she's a high-ranking god so killing her would be detrimental, but to forfeit because of such a wound disappointed me.)

Please notify me of any mistakes.