Honestly despite how fanarts depict Curren as the "devilish imouto-type" she is really a nice girl just like how her RL
In-game she at most teases the trainer but never go too far into the overly clingy or yandere trait. Although IIRC Falco does describe Curren as the "little devil" type in her lobby line, in contrast to her own "light" (pure?) type.
Rice!?Onii-chan!Rice will give herself to you as well. Take care in eating me up.Rice made some chocolate. Is that alright...?I'll be happy if you take it.Instead of chocolates,Onii-chan will have Curren instead?Onii-sama! Onii-sama!