Barth interestingly locates God’s aseity within His own existence, instead of making it depend on his relation to the world. His absolute-ness, unconditioned-ness, et al, are all something He has in His own existence.
‘The fact that in every way He is independent of all all other reality does not in itself constitute God’s freedom but its excercise.’ (C/D 2.1 p. 308)
‘…the absoluteness of God – which makes it a genuine absoluteness – does not derive primarily from the mode of his relationship to the world.’ (p. 309)
It’s in virtue of this aspect of God’s aseity – it’s non-dependence on His relationship to the world – that God can enter into a relationship to the world.