CYCLOPS

Two of the most destructive mutants alive are completely harmless to each other. Scott Summers channels concussive force through his eyes; his younger brother Alex Summers — Havok, introduced in X-Men #54 (1969) — absorbs cosmic energy and discharges it as searing plasma. Put them at opposite ends of a battlefield and each man's signature weapon simply washes over the other with no effect at all.

The immunity runs both directions and has been treated as a fixed rule of Summers biology: Cyclops's optic blasts cannot injure Havok, and Havok's plasma cannot burn Cyclops. Handbook and reference accounts extend the pattern across the bloodline's energy manipulators, noting the brothers are also resistant to each other's half-brother Adam X — while their third brother, Gabriel, called Vulcan, is the dangerous exception who can hurt them, if only partially resisted in return.

The practical consequence is pure theatre: when Scott and Alex truly fall out — over leadership, over Polaris, over the direction of mutantkind — the energy war everyone expects never happens. Two living artillery pieces are reduced to arguments, shoving and fists, exactly like any other brothers who have run out of better ways to settle a score.