It is not just a relationship. Relationship means there is this,
and there is that, and somehow this is linked to that.
Interdependent origination means THIS IS, THAT IS, they are not
separated in the first place, they do not have inherent existence
but arises as interdependent origination like the
Net of Indra. If THIS IS NOT, THAT IS NOT. THIS ARISES, THAT
ARISES. THIS CEASES, THAT CEASES. They are not two things linked to
together, it is that due to interdependent origination there cannot
be 'separate things' with inherent existence in the first place.
You need to look into the Net of Indra to have a better idea.
Emptiness does not mean a void or nothingness, it just means
nothing has inherent existence, non-existence, both existence and
non existence, and neither existence and non existence. It also
means that all things are not-one (not same), not-two (not
separate/different). Emptiness is its nature.