Shiro wanted to find out the real motivation of Xavier who now continued his walk and didn't care to answer her question. He acted as if she was not there and he still walked leisurely and didn't want to look at her.
Shiro thought this situation was really interesting and she felt even more curious because the man didn't want to show his face to her. Was he hiding something? He didn't want her to read his expression?
Shiro smiled to herself. She was suspicious that the two brothers were invested in Elena, but perhaps in different ways. She was curious to know how was Xavier invested in Elena.
After a few seconds of not getting an answer from Xavier, the impatient Shiro walked quickly after the man. That's when Xavier suddenly stopped and it made Shiro stop suddenly too.
Finally, Xavier turned to face her. Now Shiro could see his expression, and she didn't feel comfortable with what she saw.