This "brother" she keeps talking about is definitely just Nagi xD. The only thing that's still making part of me believe that Nagi has a brother, is that hair sticking out xD. But, If this "missing brother" really is a future character, then I bet you it's gonna be Segawa's fiance.
If Tsukasa just went outside or something, Idk what I might do to this author xD. But damn, though! So much information in one chapter. A lot of people wanted Tsukasa's backstory and we got a bunch in one chapter but, I guess the feels come with the package... I was expecting it, but it still...
Ah shit... My worst fear has been realized... Though, this could go two ways. Either they continue this thing that's going on and reveal who Tsukasa is(unlikely to happen), or leave it and go back to the slice of life stuff.
For example, there was a chapter where Nasa had a dream about being...