Sunfire (Shiro Yoshida) is with his uncle Tomo. He blames the Americans for the death of his mother, from cancer after the bombing of Hiroshima (which is also possibly the source of his mutation). His powers (flight and burning, basically a kind of Human Torch deal) lay dormant until he visited the city with his uncle not long ago. He and his uncle see his father (Saburo Yoshida), who they are travelling with, as a bit of a collaborator, but doesn't seem to actually bear ill-will to him.
He now plans to destroy the Capitol dome. X-Men stop him not through hitting him (although there's quite a bit of that) but by stalling him until his uncle shoots his father, which quickly resolves the issue for him.
We end with the X-Men wishing they'd reached him sooner and been able to talk him down. "Maybe the next one" they say, as they walk away, and see have two silent panels of Sunfire grieving over his father's corpse - the first emotional "beat panels" that I recall.
This more serious take on what radiation actually is and the horrors of atomic war sits a bit uncomfortably alongside the X-Men. This contrast will later be mined by Ellis's Exogenetic.