"...Morgan, are you all right? You're acting stranger than usual..." Robin was seriously starting to get concerned at this point. Sure, Morgan did do some odd things at times, but this was a new level of weird.
But as a purple light suddenly surrounded Robin's feet, she had other things to think about. "Huh?! I...is this some sort of prank?! Y-you can stop it now!" However, Morgan didn't listen. It was like she couldn't do anything but read the spell out. Her eyes blank and her face emotionless.
The light grew closer at an alarming rate, until it touched Robin's feet. Her loafers, thighs, and even her panties instantly disappeared, the light growing stronger beneath her.
"W-what?! M-my clothes! ...W...where did they go?! M-Morgan! What's- Ah!" Robin was cut off short as an odd pain ran through her legs. She fell onto her back, suddenly losing her balance. She stared back at her legs in horror, as she were slowly covered in small, pink scales. If that wasn't enough, they were starting to fuse together as well.
She was completely and utterly speechless, too shocked to even move. Her feet grew thinner, longer... Flattened out. As her legs were fused together completely, her feet looked more like the tail of a fish. It then hit her... She was a mermaid!
"M-Morgan...! W-what did you do...?!" Robin asked in fear, glancing up at her sister, who had finally stopped reading.
"...What? WHAT?! What happened to your legs?!" Morgan asked, just as confused as Robin. "...Wait... it actually worked? Eheh..." The wicked grin that appeared on Morgan's face made Robin crawl back, but her new tail was quite heavy, lowering her mobility severely. "Oh... We'll have loads of fun, sis..."