@Ghostdevil Keeping her appearance as a reliable onee-san to her younger sisters. She only shows her lax side to Haruki when he said she could be more selfish around him, thus basically making his room her private relaxation spot where she can eat snacks, read stuff, and sleep sloppily. Like what deathmailrock said too, she shares a room with Yayoi, with the twins just at the other side of sliding doors.