Okay how about this: Ayato runs every day. After hearing that Chisa goes jogging, Ayato tries different running routes to see if he can accidentally bump into her. He doesn't think much of it. It's just a silly game, plus he's pretty tired of looking at the same scene anyway. One day, he actually sees her. He's about to come and says hi, but he stops because she looks so serious and determined. He initially thought she was a frail, timid lady, but after they hung out and now this, he realizes she's really strong. Suddenly, his heart races and it's definitely not because he has been running.