Mahouka Koukou no Rettousei 08 - Recollection Chapter (novel)

The story is set 3 years before the siblings, Tatsuya and Miyuki enroll in First High School, when Okinawa is invaded. This is the moment where Miyuki starts to understand and feel far more for her brother than sibling love. It also explains some important points of what kinds of experiences Tatsuya went through and why his practical magic scores are poor.