thank you for your answer.
I do not understand how to bend the spine of the model which applied FBBIK.
I am using FBBIK Effectors.
I attached "Full Body Biped IK" to the model and set the parameters.
For example, put model's hand on the front.
Then the waist bends and the torso looks twisted.
But the spine looks straight.
This sometimes looks unnatural.
When I move the FBBIK Effectors Target in my model, the spine is always straight.
Does FBBIK (Finalik) have a function to bend the spine?
With AimIK, I understood in this video that I can bend the spine of the model.
Do I need to use AimIK to bend my spine?
I want to bend the bone like this video by moving the Target of Effectors of FBBIK.