Renderotica

If you are using the correct bones, in the correct node parenting hierarchy, you can get results.

Well quick test on G9
I (incorrectly) did null add to BRST Breast 2 (There are alot of unneeded bones on the figure ie pectoral bones on eyelashes so make sure you get the right one)
I then ik'd off that node
and parented ik chain to hand

Moving hand moved the breast but results weren't anywhere near good much better posing induvidually unless I needed to rotate my null before ik'n or something.

I dont IK chain that often so reviewed WPGURU's YT Vid (https://youtu.be/lCv_PFWcLcE)
and looks like create mid null, chain both bones, then parent both iks to null and move null was his method as well.

Im guessing you may have accidentally ik'd the wrong breast bone (figure or figures piece instead of Breastacular's Breast)

ADDENDUM:

With further testing IK was not working using that method on the Pectorals, BRST Breast, (didn't appear locked, limits maybe???) but did work for BRST Breast 2. 

Edited by user Tuesday, December 12, 2023 3:50:46 AM(UTC)  | Reason: Addendum