This is an Authority granted to MC by his reincarnator. It allows him to use the template of "human[1]" characters from fictional works MC knew from his previous life forone hour per day.
Template includes their powers, skills, combat style, experiences, instincts, and even partial memories. Using a template DOES NOT change his appearance, only stuff like tattoos or markings may appear.
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Tier System
This power classifies characters into three tiers, each with a cooldown that begins the moment Rein stops that specific template. During cooldown, the entire Path of Human God enters cooldown and becomes unusable until it ends.
Tier 1: below continent-level — 10 seconds
Tier 2: continent to world-ender — 10 days
Tier 3: "gods in human skin" - 10 years
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Conditions on media:
• Only visual, long-form depictions count (anime/manga/games/TV/ movies). Text-only works don't qualify.
• He also can't use any character he created or helped create (OCs, authored/designed characters, etc.).
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Characters he CANNOT pick:
• Characters that are no longer truly human.
• Characters who have another sentient non-human being sealed inside them.
• Characters that are avatars of gods or incarnations of divine beings.
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Retention Rule:
He cannot permanently retain any creation, enhancement, or power-up that increases his own or his allies' power through a borrowed template. All other effects and results remain.
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Trait Assimilation:
He can assimilate one trait (NOT a power) from any tier 1 or 2 character he has already used. This trait can be physical (like Six Eyes or Toji's physique), but not full power systems. So yes, he can take Gojo's Six Eyes, but not Limitless. Talents can also be taken, as long as they don't come with supernatural abilities.
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**Beyond this point is spoiler territory, proceed at your own risk.**
After Rein became the Human Devil, this Authority expanded/changed by allowing him to access human–hybrid characters as well.
[1] Read the note at the bottom after reading Arc 2.