Ty's heart was racing. He wasn't going to be a boy anymore, or even a human, but he could leave behind the unpleasant world he had known and be a beautiful mermaid! He snapped his fingers just as Larissa had and... nothing happened.
"Oh, sorry!" Larissa smiled. "I should've explained, that only works for mermaids! You need to step into the water."
"OK," Ty laughed, starting to pull off his clothes. He doffed his shoes and socks, then his shirt, undid and stepped out of his trousers, and blushed as he got to his underwear.
"Why did you stop?" Larissa asked softly.
"I don't wanna be naked in front of you," Ty replied nervously.
"I don't mind seeing your false human genitalia," Larissa retorted kindly.
"If you're sure," Ty answered, shyly pulling his underwear off to let his stiff penis out. He walked into the water, stepping in until it was almost at his waist level. "Um... how do I undo my seal?" he asked confusedly.
"Look at your chest," Larissa answered. Ty did... and gasped. The skin had turned smooth, hairless and feminine. "Your seal is your maleness."
Ty didn't need another word to tell him what to do- only instinct. His nipples had started to swell, his areolae widening around them, and he quickly brought his fingers to his chest and pinched them. "Mmmmh," he moaned as his body responded to the touch femininely. He continued to massage his nipples as the flesh on his chest expanded, C cup breasts forming as his figure reshaped itself.
His penis continued to pulsate under the waves, tingling as he fondled his feminine body. "Aaahh~" he cried out in pleasure as his body convulsed and he squirted his seed harshly into the water, every drop of semen being released from him as he fondled his chest. She felt a new overwhelming emotion as her body purged itself of maleness.
"The seal is undone!" Larissa declared excitedly. "My dear Titania, let your true body out!"
Titania moaned and writhed under the water, her skin turning scaly down her legs. Her feet melted together into her soft, elegant tailfins. Her penis receded into her skin, then her scrotum, as the space they had once inhabited vanished and her long fish tail formed from the conjoining of her legs. Almost instantly, she knew how to swim beautifully and breathe underwater indefinitely.
As her body finished forming, she sighed in pleasure, and felt Larissa hug her lovingly. "My daughter, how I've missed you!" she said ecstatically.