I'm not sure whether it's that they don't exist or whether it's that they both are without something--when I first looked at this chapter I thought Hana was talking about a lack, but then when I stared at it I thought that might be a rather limiting translation. It's a fairly wide-ranging word--though you're right that 'nonexistence' does tie back into other CLAMP works, which makes me think it was probably the better choice.

I was very lucky, and it does make me very nostalgic. Particularly this chapter, I love that restaurant. Well, and Kitano Tenmanguu too, I used to go biking around there and go to the shrine flea market every month.