Kana is the lost love of Haruhiko who is a single mother raising Natsu by herself.

Haruhiko initially left her because his parents pressured him to take over the family business. After his injury, he wanted to see her but they wouldn't phone her. To bypass this, he possessed Ichiro and went to meet her.

Kana probably caught on that it was him when he began to speak about how he had left her, right before returning to his body.