You are Yasuhiro Muto's younger sister and feel a bad premonition every time Sanzu appears next to your brother. It was like you didn't trust Sanzu at all for some reason based on your instincts

Until that day comes The sight of Sanzu coldly slashing Muto's body with his katana was like the look in his eyes

Sanzu tells Muto that he tricked your brother all this time. That shocked you to the point where you didn't dare appear from behind the container.