So here are just a few things that I want to make sure everyone understands to avoid any confusion.

Power Scale

So both worlds use different scales for power, and this is how I have placed them.

Low-Class Devil - E Rank

Middle Class - D Rank

High Class - C Rank

Ultimate Class - B Rank

Satan Class - A Rank

Super Class - EX Rank

This is how I have scaled the two power scales. A not with the Fate system, it goes E, E+, E++, so there are three brackets in each one of the ranks.

Kuro's Rank

As a base human with no class card or not fused with Magical Ruby, Kuro is :

Strength: D

Endurance: D+

Agility: D++

Mana: B

When she is using a Class card, then she takes on their parameters check the chapter called Class cards for those.

Now when Kuro is fused with Magical Ruby in stealth mode, she gains two sub ranks to all her base stats.

And in full magical girl mode, she gains an entire full rank to each of her stats.

I have done it like this so that Kuro isn't just dependent on her Class Cards, and she can get stronger via her own effort. Something I thought was necessary, or it would just be her using the Emiya card

constantly, and I wanted to do something different.

Class Cards

Class cards can be used in three different ways and have two forms of being used.

They can be included or installed.

Include: Temporarily materializes the weapon or Noble Phantasm of the hero by overwriting a Mystic Code which is Magical Ruby. Users can Include a card even while having a different card Installed.

Install: The true usage of the Class Cards installs the card directly into the user's body, granting the Noble Phantasms, Skills, and appearance and parameters of the Heroic Spirit of the card.

Magic

So the magic systems are very different in some ways and the same in other ways.

For starters, I will be calling Magecraft magic just to make it simple for everyone.

In fate, to use magic, you need magic circuits. Without them, you can't cast magecraft. That is why Kuro refers to her magic as one of a kind; no one else in the DxD world has magical circuits.

Given that Alya isn't a thing in the DxD world, it will allow Kuro to permanently trace, and project weapons as Alya isn't there to remove them.

Unlimited Blade Works will not be a one-stop shop for everything. It can only do swords, spears, daggers, halberds, sheaths of weapons, as well as shields and defensive armaments with a much higher mana cost.

It won't be pulling every Noble Phantasm under the sun like I have seen other stories do.

Other than that, magic is quite the same, but Kuro only knows a select amount of magics these are:

Healing Magic

Rune Magic

Tracing and Projection

Reinforcement

Alteration

(These three are all Material Transmutation and are what Emiya uses to make his swords, but unlike Emiya, her origin isn't locked to sword, so she can make other things through these as well)

Some Jewel Magecraft

And the Emiya Family Magic.

These are all the forms of magic that Kuro currently knows, while she can learn more, that will take a long time. There is a reason that family crests are passed down as it's an easy way to pass on spells without the need to really learn them.