Mahouka Koukou no Rettousei: Tsuioku-hen S01

Now that we look at Mio and Tatsuya, it seems like they're getting along really well as siblings. But it wasn't always like that... Three years ago, Mio was really distressed by her older brother. The rest of their family treated her like a guardian angel. But what was bothering Mio was that Tatsuya never showed any emotional expression. However, when they got into danger on their trip to Okinawa, their relationship started to change forever...