とは[裏腹「うらはら」] => Contrary to A, opposite of A, ... N1
Contrast/Surprise
[一方「いっぽう」]だ => Change A continues, A does not stop N2
Miscellaneous
[一方「いっぽう」] => On one hand A, on the other, B; Although A, at the same time, B N2
Contrast,Surprise