Sayren's eyes scanned Sekai. Analyzing her movements after the small figured woman said she would make the first strike. She hesitated, which only gave Sayren more time to think up a strategy. The woman clumsily approached Sayren, the water probably didn't help her movements, since it was about waist deep. Which meant she couldn't quite rely on her kicks as much as she would like to. That left her with quick fist strikes. Which seemed alright, because she didn't want to hurt the girl, just smack her around a little to get an idea on what she was dealing with.
A messy punch was thrown. It was off balanced and awkward. The girl must either have no real unarmed combat experience or was just off from the water obstructing her movements. With that in min, Sayren used her left arm and slapped Sekai's right arm down toward's Sayren's right. Deflecting the initial strike away from her so she could use the motion to then give Sekai an open palmed hit with her right hand towards Sekai's left shoulder.
If the girl had approached this in the manner Sayren had hoped for, the girl would most likely try to strike with her left. Mainly because kicking wasn't going to be fast enough. And because of that, striking at the shoulder so quickly would at least push her back a little, not really doing any more damage than an enforced slap. If the attack followed through or was somehow missed, Sayren would bring her left arm back up into a defensive position and draw her fist back down to her side. Awaiting for the girl's next move. "Nice punch. A little meaty, but a little bit of training can change that."