Soniona has to be the most lust-ridden pairing of all the Sonic franchise, it's almost par with Sonouge except this was canon in the comics. It'a simple, Sonic was frustrated over breaking up with Sally and was horny as fuck, so much that he betrayed the trust of his best friend and little brother for some vixen pussy. Fiona was desperate for attention from a hero like Sonic and wanted to win his trust at any cost. The things they did intimately must have been extreme, they probably fucked everytime they could at least twice a day. They must have tried all sex positions imaginable. The pairing was pure lust, there was no real love involved except maybe from Fiona a bit, but none from Sonic since he didn't really trust her. Soniona is probably above Shadally in terms of sex simply because they reciprocated.