A deeper more concentrated chakra lying within a person. It is virtually unknown to most ninja the only ones knowing about it now have barely scratched the surface of it power.
It is obtained by a fit of rage that surpasses all others, generally sparked by a memory of the past that fuels the user. Similar to the Eight Chakra Gates it has four known levels called the Five Inner Paths. No one has ever gained use of all five, and most don't even make it to the second. Inner Chakra appears as a Golden Energy.
Five Inner Paths
Inner Chakra was first used by Rokudou Sennin and therefore only he knew of its secrets, even though not even he could not master it.
Stage One- First Path
The most basic and easy form to obtain. It is obtained by a fit of rage that surpasses all others. It boosts the user's strength and speed enormously and makes their jutsu more lethal.
Stage Two- Second Path
This too is obtained by a fit of rage, but this fit cannot be pre-thought out. It must be an on-the-spot transformation that the user isn't even aware of at first. It causes the users hair to spike and muscles to bulge slightly. Their strength is increased three fold as is their speed.
Stage Three- Third Path
This form is obtained by intense training. Once complete the users hair grows slightly and spikes even more. Their muscles bulge even more and their strength and speed increases ten fold. It is said that in this form, the body is to strong and is resistant to all jutsu
Stage Four- Fourth Path
Everything about this path is unknown.