The whole theme of part2 is that fames suck, normality's better. And thus it means Denji in the end will definitely learn to settle with a normal family and live a normal life till death. And to achieve this, he'll need a true normal girl, a girl without any of devil association. And ya know, Freckles is just that perfect normal girl, who has appeared since the very start of pt2 and been having a plot armor thicker than 99% of CSM characters. Therefore, I can see there's a very VERY HIGH chance Fuji is setting up for her to be Denji's endgame wife, a real normal wife