The magic spell Gisela had originally used to temporarily turn herself from a mermaid to a male human in exchange for temporarily turning Kevin into a mermaid was only good for 48 hours. If she didn't kiss him again before that time was up they would both be stuck permanently in their new forms. Gisela hadn't expected it to be so difficult to locate Lilia and she hadn't expected Kevin would escape. Unfamiliar with Lilia's serum, Gisela had no idea how Kevin had temporarily become a human male again but with Kevin a mermaid again she couldn't risk waiting any longer. Gisela was aghast at the thought of being stuck as a human male.
There was one other reason Gisela chose to kiss Kevin. Gisela's male body was reacting to the sight of a naked mermaid.
Kevin felt very vulnerable. Here he was a mermaid out of water with a man standing over him. Kevin felt strangely vulnerable and afraid of what Gisela might do next.
Gisela kneeled on the floor by the frightened mermaid and leaned toward Kevin who leaned away. Gisela grabbed Kevin's head and pulled the mermaid in for an involuntary kiss.
There was a perceptible jolt of magical energy and Gisela could feel her body start to change. Even so Gisela held the kiss, to Kevin's confusion and distress, until her transforming legs grew weak and she collapsed on the floor next to Kevin. She had the presence of mind to remove her shorts and shirt as her mermaid tail and breasts returned.
Kevin watched Gisela changing back to the form she had prior to their fateful hot tub kiss. He should be changing back too, shouldn't he? Instead Kevin remained a mermaid as a second mermaid took form beside him.