This chapter just serves as my own personal thoughts on the power scaling between Shisui and Earthland mages. Remember, these are PERSONAL opinions. I will update as the chapter goes on.
Shinobi Ranks vs Wizard Ranks (due to the nature of Shinobi, just because someone is in "Genin", does not mean they can beat actual Genins and vice versa. For example, Erza at Regular S-class is SO NOT strong enough to beat someone like Kakashi, even at his Wave Country power level):
Academy = D-class
Genin = C-class (Romeo Conbolt probably vs rookie Sakura)
Chunnin = B-class (Natsu at the start of the series vs Lee from chunnin arc)
Jonin = A-class (Asuma vs Mystogan. This one is debatable. Asuma just never truly got to shine as an "Elite Shinobi", nor did Mystogan truly shine apart from that battle against Laxus.)
Elite Jonin = Regular S-class (Erza vs Wave Country Kakashi)
Semi-Kage = Irregular S-class (Laxus during Tenrou vs Guy)(Guy is so underrated by the way. He is literally super OP yet gets overlooked by so many people .-. But don't worry Guy, in this fanfic, I'm propping you up as Semi-kage level).
Kage = Wizard Saint (Prime Hiruzen vs Gildarts)(Wizard Saint level is not to be confused by the 'Wizard Saint' from the Magic Council.)
Super Kage = Apocalypse class (Hashirama vs Acnologia or possibly E.N.D too)
Chapter 1:
Before we begin, let's talk about Shisui himself. Personally, considering that he unlocked the Mangekyo AND Susanoo at 16, I am inclined to rank him at somewhere higher than the level of Kakashi during the Wave Country arc, but weaker than Itachi during the Naruto training/looking for Tsunade arc.
For context, this Kakashi felt pathetically weak in context of the WHOLE Naruto series, but he was portrayed as the first "Big shot" character. Itachi, with just one Tsukuyomi, took down Kakashi like it was nothing. Let's not forget that Shisui has Kotoamatsukami. But anyways, in terms of actual combat prowess, Kakashi would likely beat Shisui in Battle IQ, but in terms of actual combat abilities (and the obvious hacks that Mangekyo would provide and Shisui being a full-blooded Uchiha, making his Sharingan not as draining as Kakashi's), if Kakashi cannot end the fight within minutes, Shisui would likely come out victorious in the end.
So that's the power level of Shisui at the start of this fanfic, stronger than Wave Country Kakashi, but still weaker than Itachi in his Akatsuki era.
Chapter 5:
In Chapter 5, Warrod Sequen was introduced. His power level I have compared it to Hiruzen in his later years. At his Prime, I PERSONALLY feel like Hiruzen could wipe Warrod no problem. BUT, age is a huge thing. "Aura" wise, both Warrod and Hiruzen would likely have the same "air" to them. BUT, in actual combat, even this aged Hiruzen would be able to cause problems for Warrod. I'm even leaning Hiruzen maybe using 80% of his powers to win.
I know that the Wizard Saints are considered by the people of Ishgar to be the strongest, but let's face it. There are other mages around who are WAY stronger but not Wizard Saints either due to politics or personal reasons. Case in point: Gildarts, who by the way, I feel like would be able to take on Prime Hiruzen at maybe 80 to 90% power. But i'll officially gauge his power level in the future when he officially appears in this fanfic. But for now, let's just put a placeholder that Gildarts during Tenrou Island arc would be at the strength level of someone like the 4th Raikage.
This means that Gildarts in my personal opinion IS THE STRONGEST MAGE IN ISHGAR. He is THE top dawg. Possibly only the upper echeleon of the Spriggan 12 could contend with him one on one. Which means that shinobi on the level of the Sannin (during Naruto's time), Minato Namikaze, Fugaku Uchiha (honestly again, this dude could slap the shit out of Itachi hands down but due to reasons, he does not), Sakumo Hatake, Hanzo of the Salamander, Obito, all these Shinobi would be as strong if not stronger than Gildarts and only people from Alvarez would pose significant challenges for them (or possibly end-game Natsu).
Back to Warrod, Shisui recognizes the aura of Warrod and links it to the aura of aged Hiruzen, BUT, Shisui does not know the actual combat prowess of Warrod.
Chapter 7:
Post-training Shisui would rank somewhere near Itachi at death's door. In my honest to god opinion, ITACHI HELD THE FUCK BACK AGAINST SASUKE. Anyone who disagrees with me can shove it up their a- I mean are entitled to their own opinions. But for me, Itachi should have been able to wipe the floor with Sasuke at that point. Like come on bro it's not even close especially with the Mangekyo. "But Itachi was severely weakened and sick" yeah yeah yeah. Let me live in my fantasy. Sasuke should have lost spectacularly, and he STILL LOST BY THE WAY EVEN THOUGH ITACHI WAS SEVERELY HANDICAPPED LMAO.
Okay enough of that short rant, yes my Shisui would be somewhere on that level of Itachi, which is still weaker than the Itachi from the earlier arc. Itachi would have gotten weaker as the years went by due to his illness, and I feel like Shisui would only attain this level after more development.
By the way, if Shisui fought against Warrod at this point, I feel that barring the use of Mangekyo and Susanoo, Shisui would have a relatively hard time. Warrod would have had YEARS of combat experience and battle awareness to know that after the first body flicker, he would be able to just "Goku" the hell out of it and "predict" or "feel" where Shisui would be.
Even with the Mangekyo, it may still be a hard fight because the only known Mangekyo ability of Shisui is the Kotoamatsukami, which I have already established would be useless since Earthland natives have no Chakra to manipulate. The only way that Shisui would stand a REAL chance to put up a fight is through Susanoo (remember, at this point he is still only at the level of the death's door Itachi). And Warrod uses Green Magic, which means trees, which means I could very easily have a Hashirama second comi-
:D.
Chapter 10:
This chapter introduces Ultear Milkovich and Meredy. Meredy would likely be somewhere in the High Chunnin to Low Jonin level. Maybe a Tokubetsu Jonin. Ultear on the other hand, is in the Elite Jonin category in this fanfic. She is still weaker than Shisui as of Chapter 10, but due to the nature and mastery of her magic, she is able to sense space-time related abilities. Which is why Shisui was caught as off guard as he was in Chapter 10.