I thought I had Shiro on a top bunk?
That could be my mistake but I distinctly remember on the first night after the infirmary incident that Gren couldn't find Sapphire cause her semblance was active as she slept so he went off to look for her the entire night. That morning Sapphire woke up from a nightmare by activating her daggers and stabbing into the bunk above her. Which means that had to have been Gren's bunk otherwise someone wouldn't taken two blades to the back.