I really love some of the class features you've come up with. Weapon Chakra, Soul Detection, and Meister's Weapon in particular are interesting.
Is this an untyped bonus? If so, the bolded line of text (emphasis mine), is unnecessary.
What do you mean by "extra x essentia invested in weapon"? Is this an increase in the weapon's essentia capacity, or a temporary booth in the effective amount of essentia invested in the weapon?
You don't need to specify the bolded part.
This is awesome.
How much do the ability scores of the weapon increase by (and when), you didn't specify.
EDIT: Also, here's a similar base class by the Demented One which you might want to check out. Perhaps you could do something similar to his Bound Strike and Bound Stance abilities when it comes to the Meister's Weapon Chakra ability? Gaining benefits based on the chakra slot being emulated would be nifty.