I picked this up a few days ago on the mod browser and all around had fun. Some notes & suggestions~
A slight compatibility issue. If it costs mana for any reason(EG: "More Modifiers" mod giving it "+% damage but costs +2 mana") if you run out of mana, it'll zap all of your ki. Not really a problem, but might help with bug reports if you catch someone complaining about a similar issue.
Lore-wise, Shouldn't Kaioken *give* you ki? It rapidly increases the concentration of Ki in the body in exchange for putting a great deal of pressure on the user.
"Aura Change Items" from Budokai Tenkaichi 3 would be awesome - some customization.
In the pre-hardmode, I feel like I spend MOST of my time charging ki. A way to passively charge Ki, even at a cost, would be very much appreciated early game. Maybe a potion or accessory that generates ki over time? This would make killing bosses w/ Ki weapons only more feasable, as well.