How could the videogame
Sonic the Hedgehog become a Nintendo franchise as opposed to Sega? If this is ASB, I apologize
I'll take a crack at it.
Sega and Nintendo, for most of their history, were engaged in a struggle for video game dominance. Well, not really, that implies that Sega was actually a threat to Nintendo, which it wasn't.
But Sega and Nintendo competed for market share. Around the time Sega came out with Sonic the Hedgehog -ironically- was the time that her days were numbered {for reasons unrelated to Sonic}. Nintendo was killing it slowly for years; Sony delivered the mortal blow with the PS2.
What then happened is Sega clung on to life long enough to find someone to buy the company. At this point Sega was on the verge of dissolution and partition between various game companies. The interesting thing is that none of those companies were called Nintendo. As Nintendo seemed completely uninterested in buying up Sega or its licences.
This has a lot to do with the fact that Sega has previously announced it would become a third-party company; Nintendo probably didn't see the need to buy Sega and probably didn't want another mascot when it already had Mario.
So, to change this you need three things, I think. One is for Sonic to be less of a household name so it won't be as awkward to see him as a major Nintendo franchise. Two, dissuade Sega from offering its services as a third-party company, so Nintendo might see a reason to take Sonic for itself. Three, make Sega more destitute than she already was, so that Sega would even consider selling Sonic.
Two and Three kind of conflict, however.