So we know of atleast one instance a Nuke was used by Morgan to kill a Skinwalker.
It's widely theorised Kemmler was nuked atleast once.
What if Eb's Kenku favour was that Eb warned and prevented the Kenku being killed by one or both of the Japanese Nukes?
It''d fit with the scale of the favour. Kenku Army for preventing Kenku Genocide.