I can see why you might think of ju based on what I wrote but yielding is not quite the same IME, the yielding I'm talking about is more akin to the idea that aiki is non-dissent, accepting the attack in other words, not the idea of pulling when pushed, pushing when pulled etc. Perhaps it'd be better to phrase it as offering no opposition to the force being directed at you, rather than moving away from a force directed at you.
Hmm, I don't recall saying anything about pulling when pushed or pushing when pulled. I think what a willow branch does is entirely different. Did you read HIPS?
I don't think merely offering no opposition gets you to a state of investment. You need to actually absorb the energy somehow, or some of it. Then you give it back, plus perhaps some of your own. I think this is what the investment in loss thing is about.
I think this might be different than aiki, actually. I think of aiki as more of an instantaneous feeding back of the energy, but you send it back along a different line than it came in on. There is no investment, its hand-to-mouth, cash-in cash-out.