When Kasumi says she wants a vacation in Tokyo, Nerima is
a district of Tokyo, so you might want to change the city, since that's
not really such a big deal, to go to Tokyo for them.
Kasumi, Mariko's best friend? Since we never see Mariko in the
series/manga, you might want to come up with a side story explaining how
they became friends and kept in touch. You mention that Kasumi wrote her
letters, but the conclusions that Mariko comes to do not seem like the
kind of stuff that Kasumi would write (specially Akane's personality).
Plus, she seems to know a LOT about the current events, and apparently
knows Akane quite well. That just begs the question: How?
Anyway, since there is a pregnancy in the plot, keeping track of time is
important. How long was the vacation? I'd be guessing maybe a week or so,
but since she might start showing pretty soon, it'd be best to know how
long she was away.
-DangBat