Johnny was transfixed by his now older... step-sis? It didn't feel right with the feeling in his... Amy had did something to him and he could feel his body growing but his dick felt limper. Johnny looked down and could see his body growing as puberty was raging through him and... was his nipples getting... bigger and tenting his shirt. As Johnny's dick was turtling into him he knew what Amy had done as his thighs and hips thickened and widened as his shorts started splitting at the seems. The internal shifts were impossible for Johnny to feel but that didn't stop him from feeling odd as his body wasn't just being sped up on it's normal trajectory, but growing in ways it normally shouldn't. In ways that Johnny hadn't felt as normal or right for him as large breasts were growing from his chest.
The picture of his mother didn't show much and he didn't have much memories of her figure or anything, but she was a Lovely woman and the female Johnny had taken after her quite a bit as the shirt for a tween hugged the now young woman's breasts tightly and a decent amount of underboob had escape. The shorts broke and his briefs were stretched to capacity. As the changes ended Johnny said "What the heck Amy? I thought... you were just going to make me older!"
"I was curious, and you got BIG."
"Well excuse me while I go find something that'll fit me." Johnny said as she waddled out of the room, and in minutes she came back in wearing her father's baggy sweats... No bra considering she didn't want to go through Maeko's underwear, and she didn't think Maeko had cups that would contain her breasts... really she wasn't wearing underwear at all and when Johnny got back she had found that Amy had...