Emiko is the Straw Hats new doctor after Chopper died. (He saved the crew but not himself.)
She used to be Boa Hancock's strongest warrior, but she was forced to go with the Straw Hats, since Boa likes Luffy.
She has a hard and cold personality. But once in awhile (most of the time with girls, Zoro, Franky, and Brook) she'll smile and laugh.
Sanji: She doesn't like Sanji that much since he makes goo-goo eyes at every pretty he sees, but still has respect for him (since he does make her dinner). Sanji has a crush on Emiko (often calling her Emi-chan most of the time and flirting with her a lot which ticks Emiko) because of her nice body.
Zoro: Zoro and Emiko are on good terms making Zoro one of Emiko's first best friend that's a man. (Besides Ussop) But she doesn't know that Zoro likes her. (He likes her because of her hard personality)
Nami: Emiko treats Nami as if she was her little sister. Nami often calls Emiko, Emi-oneesan.
Nico: Emiko looks up to Nico as a role model. Thus they get a long fantastically.
Luffy: Luffy thinks Emiko is too harsh and should be a lot more like him, while Emiko thinks Luffy is too childish and should be a lot more like her. Let's just say, they can set of a bomb in one room.
Franky: Franky is Emiko's subsitute older brother. And body guard.... He always punches Sanji whenever he catches him flirting with Emiko or looking at her because he's checking her out.
Brook: Brook creeps Emiko out but she likes him (as a friend) because of his musical talents.