okay i'm double posting sorry, but here is my idea!
my male character is a little based off the doctor from doctor who--he's a playful, incredibly silly, awkward, slightly insensitive, brilliant guy! he looks out for everyone he can, especially his little sister, and if s**t goes awry, he takes it very, very hard. it's not pretty at all. so he has this crazy happy energy around people, but then on his own, he's frequently a little somber. he just has the weight of the world on his shoulders, because he is basically on his own in the world with his younger sister, and he wants to ensure no harm befalls her. and she doesn't exactly make his job easy.
for the younger sister,
i think i'd like something bad to befall her in the course of the story line, because she is basically her older brother's world, and i think that'd be very interesting for his development. if they were separated, then she'd have a chance to kind of stand up for herself, and discover who she really is.
but for her, i'm thinking--let's make her a handful. like, rebellious as ********, always flirting with everybody, always getting up to no good. of course underneath it all, she's a great person, but she's just having fun. And she loves to piss off her older brother--so his advice rarely gets followed. it's not because she doesn't love him, but because she hates rules. she's going to be strong and brave as ********, but also pretty insensitive and while she can be courageous, she fails to think things through fully most of the time.