...your girlfriend/sister is wearing a shining cute blue prom dress.
"So, like, what do you think about this, bro?" your shapeshifting girlfriend/sister asks you while she's moving her dainty hands, tipped with fitting blue nail polish across her new curves. "Because I think this dress fits me super well... Teehee".
Your jaw drops as you look at her as she looks like drop dead gorgeous in that blue prom dress... You have never thought of your sister this way before, but here you are now. Noticing your shock your shapeshifting girlfriend/sister takes advantage of the situation, and starts walking towards you slowly, swaying her hips and leaning towards you until you meet her light blue eyes, lacking of betraying any sign of intelligence. She closes you mouth gently with a dainty finger and kisses you, and then asks "Bro? Like, are you okay? Did I make you shock?"
"N...no, not at all, 'sis'. It's just that I saw you look kinda cute on this dress." you awkwardly answer her that your shapeshifting bratty, but cute sister.
"Teehee, thank you, bro." your shapeshifting girlfriend/sister smiles. "Anyway, bro. Like, what should we do next?"