User blog comment:AquilaeAltair/OnS Theories. Fourteenth Theory - Shiho Kimizuki. A traitor or a person who understands the situation the whole squad is in./@comment-36009152-20190830230555/@comment-36009152-20190904183608

Then there is trying to see the point of view of the characters as well. Like with Kimizuki he may just be afraid and rightfully so, having an experience of seeing someone murder everyone in a room just like that, and escaping, no one can blame him for just wanting to rescue his sister.

The 'worst' case is that he gets his sister to safety and joins the squad later, sure a best case actually but not if people need him to rescue Mirai then find the squad to all escape. It will likely be that, all that needs to be done is find Mitsuba, as for Yu and Mika they should be able to locate them fine once Yu has been freed.