Explanation of Flying Thunder God
After writing it, I read it over and wasn't very satisfied because there were too many details I had thought of. I felt like I had forgotten something.
When I started writing the book, I thought about the Flying Thunder God for a long time. When I saw the Flash, many readers said that the Flying Thunder God relied on spatial talent, which surprised me because I thought the idea of spatial talent was simply not feasible.
The situation of those three Fourth Hokage guards is unavoidable. Unless you choose to ignore it, it's impossible to explain why these three "weaklings" have spatial abilities, while other top geniuses in the Hokage lineage don't, and not even so many ninjas in Konoha.
But since we've ruled out the spatial talent theory, I can't just kill them and leave the rest unresolved. I need to explain all the special cases of Flying Thunder God. I don't know if I've missed anything, but I'll list the ones I remember. I'm a bit groggy from typing so late:
[Regular flight can be disregarded]
[Explanation of the Flying Thunder God Technique: Based on the characteristics of those three individuals, the principle of multitasking is derived.]
[Explanation of Flying Thunder God's chakra consumption: It's a two-stage consumption process, which explains its use for Flying Thunder God Guiding, normal movement, moving the Allied Shinobi Alliance (its size is such that it squeezes everyone together, probably still smaller than the Ten-Tails' Tailed Beast Ball), and long-distance teleportation.]
[Explanation of why the Second Hokage died: 1. Carrying someone while flying consumes a lot of energy (later, he could only carry Sasuke for very short distances) because he used the unimproved Flying Thunder God Technique; 2. He always placed his seals close to his body on Kunai, so even if he placed one in Konoha, it would be impossible to fly back, let alone leave seals along the way. It's normal that he was surrounded and died; there was no plot-driven death.]
[Because the death of the Second Hokage needed to be explained, and the technique required chakra, a battery and signal tower were installed. This also explains why Minato was a step too late in supporting his own team (he had already done his best; sensory range is limited, and running to multiple battlefields continuously was incredibly demanding).]
[Explanation of why the jutsu on a person doesn't disappear: Improved or basic version of the Jinchuriki sealing technique]
[Explaining why other top ninjas in Konoha didn't learn it: In the past, Flying Thunder God was basically only usable with Taijutsu, and these Ninjutsu styles would rather focus on improving their Body Flicker Technique.]
[The time it took to learn the Flying Thunder God: Minato's strength can be roughly deduced from the original work: when fighting Kishimoto, he wasn't fast enough, otherwise he wouldn't have needed to fly up the tree, he could have directly flown onto the floating Kunai; his strength may have improved further at the Kannabi Bridge; he further refined it when fighting Obito (Rasengan + Flying Thunder God). From this, we can roughly infer the learning time: even if the protagonist's talent is superior after stat increases, it is estimated that he could completely replicate all of Minato's fighting styles by around the age of 20, which also includes the prerequisite of Fuinjutsu.]
[The research time mentioned above also indirectly explains why other members of the Hokage lineage didn't study it—it took too long.]
[In the Minato vs. Obito speed battle, there's a bug in the TV version. In the original manga, the sequence is: throw Kunai --> transfer + Rasengan hit --> follow up with Kunai; in the TV version, it's: throw Kunai --> transfer --> grab Kunai --> swing arm --> Rasengan hits. This timeline completely exceeds the opening moment when Obito dodges Minato's counterattack. The TV version sacrificed realism for the sake of visual appeal.]
[Explanation of the final, extremely long-range perception of displacement: Konoha has a large Barrier.]
There's anything else I can't think of right now, I'll add it later when I remember!