When those still loyal to the Empire were forced to evacuate after the Empire's fall, little baby Hux (only 4 at the time) somehow got separated from his parents and was left behind.
Cut to Han (or Chewie) finding a redhead kid, dressed in typical Empire fashion, hiding in their cargo hold, crying his eyes out.
Han: Well.... shit.
+ Han (and Leia) DO try and find the kid's parents but he only knows them by "Mama" and "Papa" and only knows his first name (or maybe pronounces 'Hux' wrong so that's no help) + Hux basically imprints on Han/Chewie and cries whenever they leave. + Han, Chewie (and Leia) don't really want to give the kid back to what's left of the Empire (who knows what they'd do to him!) + Hux and infant!Ben
Gen AU - Han accidentally adopted bb!Hux
Cut to Han (or Chewie) finding a redhead kid, dressed in typical Empire fashion, hiding in their cargo hold, crying his eyes out.
Han: Well.... shit.
+ Han (and Leia) DO try and find the kid's parents but he only knows them by "Mama" and "Papa" and only knows his first name (or maybe pronounces 'Hux' wrong so that's no help)
+ Hux basically imprints on Han/Chewie and cries whenever they leave.
+ Han, Chewie (and Leia) don't really want to give the kid back to what's left of the Empire (who knows what they'd do to him!)
+ Hux and infant!Ben