若葉の季節 いとこって・・・?

I liked her since I was a kid, but I couldn't say it because I was so stubborn.
But ... I still love her ...

Keiichi and Natsuko, cousins, are next to each other in the same apartment. Keiichi had always liked Natsuko, but he couldn't show his attitude of "like" because of his original, stubborn personality. However, one day, he discovers a ring on Natsuko's left hand. "Natsuko-san ... goes to another man ..."