The couple just enjoy innocent love - what's wrong with the way things are between them? Consider also that the two are Japanese - do some research on these people (Japanese man Yuta on youtube does interviews on such subjects for example) and you'll understand that they're not "that good" when it comes to expressing feelings (Family relationships are certainly different from U.S, EU). I, for once, never thought Nishikata was "virgin-like man-child"; he's shy, loyal and respectful to his wife - that's it. It all comes to perspectives and personalities i guess, but such relationship IS possible - even though it's certainly rare and/or different i guess, especially for westerners.