Jiraiya's Imperfect Sage Mode Still Solves the Moving-Target Problem
SPOILER!
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Partial Transformation · Fukasaku & Shima · Continuous Natural-Energy Gathering
Jiraiya never reaches Naruto's clean balance, so Sage Mode visibly alters his face, hands and feet. His workaround is just as important as the imperfection: Fukasaku and Shima fuse to his shoulders and gather natural energy for him while he keeps moving and fighting, something a lone sage normally struggles to do once stored energy starts running out.
Why it worked
Jiraiya turns a weakness in his own senjutsu control into a three-person system. The elder toads are not decorative summons; they are the reason he can maintain Sage Mode during an extended battle.
Senjutsu Is a Three-Way Balance
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Physical Energy · Spiritual Energy · Natural Energy
Sage Mode begins with a deceptively simple rule: natural energy has to be added to the user's existing physical and spiritual energies in the correct balance. Too little natural energy does not produce senjutsu chakra. Too much overwhelms the user and can trigger animal-like transformation or petrification depending on the training method.
WHY IT MATTERS:
The difficulty is not finding natural energy. The difficulty is mixing exactly enough of it into chakra while staying alive and functional.