Jeez Imoto is scary. It seem that Marika had some light trauma in the past that made her think that being straight is "normal", maybe did she kiss a girl back then, also i did spot a kyun moment on Marika, maybe she will fall for real for Lily.
Half the fun is all these things that should happen but won't for a long time. Lily confessing, anyone? And half is watching--and anticipating--how things are going to go so damn wrong.
Well yeah don't assume since the author is responsible of Idol Pretender so we can't be really sure it will end yuri. I don't think Imouto is siscon tho because if it was the case she have maybe be more clingy to Marika. Here Imoto is just in shock that her sister has been replaced by another version of her.