Your nen… if you have quieted your nen inside your physical body, then there will be no re-incarnation… Once you start in on this purification process, this misogi, then you are on the way back to your original beginnings. And it follows naturally from this that, in respect of this, your budo shugyou: if your nen is in musubi with any kind of selfishness, then you will not be able to focus, and you will not make any progress. This would be bu that has gotten onto the wrong path. And if your nen is linked to your mind – but there is no connection to the body, then nenpi-kannon-riki will not arise. But if you can break a tachi or a katana, using the divine spirit of true emptiness – centered in the ki of emptiness – then it is with nen-power that it has been broken.
– – – O’Sensei, Aiki-Shinzui, p.80-81