His [Aura]

Aura.

A natural energy born from one's subconscious mind.

Every Aura varies from person to person and there are countless 'types' to an Aura.

Just like how every being has its separate mentality, goals, beliefs, ideals, and such, every Aura has separate characteristics that show just what kind of person they are.

Although we can't guess everything about the person from their Aura, we can guess some things at the very least from the characteristics.

Like the form of Aura.

Is it dense? Is it burning? Or is it fluid? Maybe gaseous or wild like a wind? 

Is it like melted metal? Or just plain Aura gained from normal training or without knowing?

There are many who reach [Rank-3] and achieve the Aura, but not that many that we could see everywhere.

A handful of strong can achieve Aura and a handful of them have a deeper characteristic.

An Aura is mostly an energy form, just like Mana.