Sam continued pleasuring Billy when their legs fused together and they moaned each beginning to move them like a tail.
"Oh that feels so good!" Billy exclaimed. "Infact I'm not wanting to live on the surfuce much anymore.
"Took you long enough." Sam replies as the two noticed their feet had become one singular fin and the scales were now up to where their knees would be. Sam sporting blue scales while Billy had green. The changes making them hornier and causing them to kiss more passionately. "Billy, we each have to complete the change now"
"Go ahead, make me a full merman." Billy said.
"Of course." Sam obliged as he placed his penis in Billy's butt and released his aquatic seed turning him fully into a merman as he moaned again now having a tail from the waist down at which point he did the same to Sam who also moaned in pleasure.
"Oh wow!" Sam shouted. "Now we're mermen!"
"Yeah, it's so cool." Billy replied as the two returned to pleasuring each other.