It'a bit longer than my usual ficlet but I'll try :)
As for the place of this story in our Sandbox universe it happens before Kaoru's birth, in Kurosaki's house. Byakuya's second pregnancy was more difficult than the first one (because his body tried to reject it), so in its seventh month he moved in the Kurosaki Isshin's house, because apart from Unohana (and Mayuri, but you wouldn't like Mayuri to examine your unborn child) he's one of the best shinigamis who also have some medical knowledge and skills. But of course, even after moving into this house Byakuya is too proud to ask for comfort and help and one night he can't sleep because of pain and loneliness and wanders around Isshin's house...
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As for the place of this story in our Sandbox universe it happens before Kaoru's birth, in Kurosaki's house. Byakuya's second pregnancy was more difficult than the first one (because his body tried to reject it), so in its seventh month he moved in the Kurosaki Isshin's house, because apart from Unohana (and Mayuri, but you wouldn't like Mayuri to examine your unborn child) he's one of the best shinigamis who also have some medical knowledge and skills.
But of course, even after moving into this house Byakuya is too proud to ask for comfort and help and one night he can't sleep because of pain and loneliness and wanders around Isshin's house...