1. Was Mei Terumi's Kekkei Genkai fire-and-earth Lava Release?
Answer: The official Naruto databook, Jin no Sho, explicitly stated that the Kekkei Genkai Mei Terumi used was Lava Release, not Lava Release.
Everyone other than Mei Terumi used Lava Release; Mei Terumi alone could use Lava Release.
The two used different Chinese characters, so please distinguish them carefully.
Lava Release was a fusion of fire and earth, producing things like magma and volcanic ash.
Lava Release was corrosive slime.
Of course, the original never stated that Lava Release was a fusion of water and earth, either, but given that slime was a liquid and pale green, a water-and-earth fusion was more likely than fire and earth.
Here was an additional list of some Kekkei Genkai.
Ice: wind and water.
Scorch: wind and fire.
Lava: fire and earth.
Magnet: wind and earth.
Storm: lightning and water.
Explosion: lightning and earth.
Wood: water and earth.
Boil: water and fire.
Dust: wind, fire, and earth.
At present, the two combinations of wind and lightning, and lightning and fire, still had no clearly defined results.
Without defined results, there was room to let the imagination run wild.
I previously wrote a Naruto novel in which I established Light Release as lightning and fire; for this one, I chose wind and lightning.
2. Regarding Genjutsu: was the Eight Gates Released Formation immune to Genjutsu?
Answer: The Eight Gates Released Formation was not immune to Genjutsu, but it should be able to weaken it. Genjutsu essentially interfered with the flow of chakra, whereas the Eight Gates Released Formation unleashed chakra within the body.
And if someone opened it to the Eighth Gate, with their chakra completely running wild, excruciating pain throughout their body, and their mental will focused to a single point, it should be impossible for them to fall under Genjutsu. For example, when Might Guy fought Six Paths Madara, Madara never used Genjutsu from beginning to end.
Besides possessing the Eight Gates Released Formation, the protagonist also possessed the power of vibrations and could easily restore his chakra flow to normal, so ordinary Genjutsu had no effect on him.
Of course, the protagonist at his current stage could not simply be immune to Genjutsu such as Tsukuyomi, Kotoamatsukami, and Infinite Tsukuyomi, but he would certainly consider this issue. Once he became strong enough, he would seek ways to counter these absurdly powerful Genjutsu.
Genjutsu involved not only chakra but also the soul. Orochimaru created a major flaw in his own soul, so Itachi's Genjutsu defeated him almost instantly.
Then, reasoning in reverse, could we take this to mean that someone with an extremely powerful soul could tank Tsukuyomi?
Besides that, there would also be Sage Mode, deeper levels of opening the Eight Gates Released Formation, opening the final two gates in the brain, further development of the Quake Release Kekkei Genkai, and so on.
3. Regarding whether Naruto existed.
Answer: At this point, the story had not even reached the Second Shinobi World War, so it was too early to bring up Naruto directly.
Besides, I had not yet fully settled on the main storyline in the later outline and would continue trying to revise it.
Explaining this issue would involve some major spoilers, so there was no need for everyone to worry. As long as the current story was enjoyable, just keep reading.
4. Ninjutsu power and ninja classifications.
Answer: The original certainly had no classifications such as low, middle, and high tier, and that included ninja-there was no designation of Kage Level, either.
I only established these classifications to make it easier to distinguish the power of various Ninjutsu and describe them more simply and conveniently.
A C-rank Ninjutsu used by a Genin and a C-rank Ninjutsu used by a Jonin were obviously different in power, right?
And some genius Genin might use a C-rank Ninjutsu with power comparable to one used by a Jonin.
I could hardly write, "So-and-so used a Jonin-level C-rank Ninjutsu..."
That would obviously make a mess of things.
So the simple classifications of low, middle, and high tier made things easier to understand and distinguish.
Moreover, these classifications were also from the protagonist's perspective, not entirely from my perspective as the author.
Simply put, if we transmigrated there and became the protagonist ourselves, we would also give Ninjutsu simple classifications that we could understand.
5. Shadow Clone and Multi Shadow Clone.
Answer: Shadow Clone was a B-rank Ninjutsu, while Multi Shadow Clone was an A-rank forbidden technique.
The protagonist only learned the ordinary B-rank Shadow Clone. The A-rank version was in the Scroll of Seals, which the protagonist could not get his hands on, either.
Furthermore, Shadow Clone was the foundation of Multi Shadow Clone. Without the ordinary version, where would the multiple version come from?
Multi Shadow Clone necessarily included the training method for ordinary Shadow Clone.
That was how Naruto learned it in one night.