I think I know what that might be... Does your model have both a motherbone (全ての親) and a... I think it's 'display center' but I usually call it 'heart bone' (操作中心)? Make sure you have both and check how they're connected to each other.
It has no axis limit on it but I cannot find the Heart/操作中心 bone you mentioned. She has a motherbone, and a groove bone, thats all I am aware of.
I just overhauled the rigging on a model yesterday and my best advice is, find your absolute favorite model with the best rigging ever, and see what's connected to what in what order, then do what you see. If you're missing some bones, make them with the + tool and copy the names. I can't really help more without seeing the model itself.
Would like me to send it to you if I can't pull it off?
Yeah, sure!
Sent it in a note! thank you so much!