The power of the Four Red Yang Formation was beyond doubt!
If one relied solely on chakra-based attacks, then even energy on the level of the Ten-Tails would find it difficult to break through the Four Red Yang Formation's defenses in a short time.
In the original timeline, the four reanimated Hokage had used this barrier to trap the Ten-Tails.
Even when the trapped Ten-Tails fired a Tailed Beast Ball whose chakra shape transformation had been pushed to the extreme, it still failed to breach the Four Red Yang Formation. Instead, it ended up battered and filthy from its own Tailed Beast Ball.
This showed that unless it was a space-time ninjutsu capable of directly distorting space, such as Kamui, or a special-natured attack such as All-Killing Ash Bones or a Truth-Seeking Orb, there was nothing that could deal with the Four Red Yang Formation.
It truly was the strongest defensive barrier that could be deployed below the Six Paths level.
Precisely because the Four Red Yang Formation was dozens of times more durable than the commonly seen Four Violet Flames Formation, its activation requirements were much more demanding as well.
The Four Violet Flames Formation could be activated with only four Chunin-level ninja, while rumor had it that the Four Red Yang Formation required four Hokage-level ninja working together.
Of course, that was merely a somewhat exaggerated claim.
As long as they were sufficiently proficient in Sealing Jutsu, four Elite Jonin-level ninja could jointly activate the Four Red Yang Formation. However, the stronger the casters, the stronger the Four Red Yang Formation they deployed. If four Hokage truly joined forces, trapping the Ten-Tails for a short time would be no problem at all.
Hyuga Kagami did not need a Four Red Yang Formation powerful enough to trap the Ten-Tails.