What Makes a Girl

Riku is a fellow aficionado of all things cute, and his own looks are even more adorable than a girl's. We're so close that people often ask us if we're dating, but I don't think of us as "a man and a woman" - he's just my beloved friend. But then one day, after we both got hit on by some menacing guys, something in our relationship started to change... This isn't the Riku I know. But then why does he make my heart flutter?