That's the first time that Martha's seen Fuminori smile, and she feels a small victory at having managed it. Maybe it's because he's becoming more comfortable around her, but either way, she's glad for it.

She's surprised to find that he would have that much faith in her, and as they continue up the stairs Martha just shrugs. "I don't know about that. It's different when it's just pretend, isn't it?"