What I heard Ikeda Sensei say a lot was "unity". Musubi, to connect and join centers.
Not sure how that translates to chinese internal terms.
There's no difference between the principles of "internal strength" in Chinese and Japanese martial arts anymore than there's a difference between the principles of swimming in China and Japan. There may be some stylistic flairs in swimming and I.S., and of course different levels of ability and understanding, but the theories are immutable. When you hear someone indicate that they think there's a difference, all they're telling you is how much they know (not much).
Notice that I used an example of an ice-block in the first post and I said to extend the arms, etc., so that there was a solid connect between the ice-block and your center. A solid connection between your center and someone else's center (or an object's center) makes you both into a "unit". That is "unity"
There are two ways to form a solid connection: one is 'through the bones' and the other is through the connection of the body. The ideal connection also always includes a connection from your center to the ground so that the stability of the ground is where you source your forces.
If a partner pushes, grab-pushes, or strikes you and you allow that push/strike to go through your bones to your center and on freely to the ground, you and your partner become one object and your middle can control the consolidated 'unit'. If there is not a solid connection, obviously you cannot reach your control through to their center (or head, or wherever.
If a partner pulls you in some manner (or you pull slightly when he grabs you), you can make a connection from your center to his/hers through the 'connection' of the body (you must keep a slight connection at all times).
That's unity. However, it's like learning to "control with the hara"... if you don't know how to control with a good connection/unity via your hara and you just try to use arms, etc., you'll miss the target and you won't really be using good kokyu.
If you look at some of Ikeda Sensei's demonstrations, you'll see that he makes sure that he has a good connection. Sometimes the connection can be a little iffy and solid in such a narrow direction that the availability of controls is limited. That's when an overly-cooperative Uke can pay off, but the theory should be pretty obvious: make a unit connection; move the combined unit with your middle. That's what Ikeda Sensei keeps saying (he's said it for years, from what I've heard), although granted some of these things are subtle enough that you need someone to show you the first steps in a careful and expanded way.