I have a bold theory that isnt some joke. I legit believe Yuji marries both Ozawa and Nobara. The reason I came to this conclusion stems from the fact that Yuji is pure and wishes to be surrounded by people he loves. Nobara and Yuji have always been 2 peas in a pod while Ozawa had a 1 sided crush towards Yuji and Nobara has shown to feel jealous of Yuji potentially having a partner before she does. Nobara and Ozawa became close friends in the end thus making all 3 tight friends which we don't get to see much together post end of the manga. Since currently its the future I can see Gege making polygamy legal thus allowing Yuji and Nobara to become prevalent in the story without making up some random partner for Nobara. It keeps everyone more bound together for convenience.