User blog comment:Xilinoc/Ch. 678 - The Future Black/@comment-3423279-20160617010144/@comment-5398287-20160618162821

Not until it's hooked up to Ichigo's crotch will the chain be truly complete.

jk but seriously, I think it's supposed to connect to something more symbolic than another part of the blade, unless of course it's representing the bond between the Quincy and Hollow/Shinigami powers.