Does Boa Hancock count as a "minor" character now that she is currently the closest character to Luffy? Hahah. Maybe I just overestimate her importance.
I really just admire the way Oda is using her character in the story in such an unexpected and interesting way. She is a cruel, proud shichibukai... but succumbs to Luffy (who never shows any sense of sexuality at all) out of a little crush. She had never experienced love for the first time, and the only time she ever felt a positive feeling toward a man was to her savior Jinbei. It seemed like destiny, almost, for her to fall in love with Luffy... Needless to say, I saw it coming. Zoro, Usopp, Franky, Brook, and especially Sanji all have their own distinct responses and attitudes toward women... Luffy shows no discrimination to either sex and will protect anyone he considers innocent, or a nakama.
Luffy doesn't even realize his own unconditional protection and pure-heartedness, so the way he treated the women in a non-sexual way was liberating for Boa... Lo and behold, she finds herself swooning over the only man ever to exist that wasn't attracted to her. It's such a unique situation, and it brings out her true colors. Even the most independent, powerful, and cruel woman could exist in Boa Hancock... but because women are born as relationship-oriented beings, even she could succumb to love.
Besides her, I am also really big fan of Buggy.