something that strikes me from the windbreaker manga is that Sakura recognized Suo as strong before ever seeing him fight and then it made me think of how that could be. . . and
in this moment Sakura recognized Kiryu's sister as strong just from this one look and well (please excuse the poor quality google is shiiiittt and I had to get crafty.)
This is what Sakura saw when he first entered the class 1-1 for the first time, with Suo literally being one of the first things in his eyeline. He smirks because he recognized something in his gaze that told him he was strong... and of course we get Suo's face after he notices Sakura, but he probably didn't think anyone was paying him any mind. I just.... my brain wants to make connections so badly. Plus the fact that Kiryu's sister is very similar in the way that she tells he brother she is fine all the time, is always smiling and teasing. Just.... I'm chewing at the bit for morrrrreee.