HG Graham's Custom Union Flag II (GN Flag)
This is my absolute favorite mobile suit from the 1st season of Gundam 00!
I was ecstatic when it was released on Premium Bandai lol
I really like its slender silhouette, even though it's humanoid, with its thin limbs
Also, the crazy specification of forcibly installing a pseudo-solar reactor originally intended for the GN-X into the Flag is a major selling point for me.

I've been wanting to meet you, Gundam!! (HG GN Flag) | ぬわし's Gunpla works