Future Reference to vampire bat transformation for size and look, except a bit bigger.
Ricky and his 15 year old little sister are very close siblings, most of that cause is from the age gap of her brother being 25 and mature, and always looked out for her and spoiled her both with things and being real affectionate. Also big factor is that their parents arent affectionate much and dont give much praise to her so it was only natural she would turn to her brother who is affectionate and gives her the attention she needs. Also, by time she was at an age to where she started to appreciate and need his company, he was already out on own in a decent sized home with just one queen sized bed and one master bathroom with a jacuzzi in it. His sister had to take full advantage of the time when he is over visiting for dinner and him seeing her, plus he lived about twenty miles away.
Ricky's family belongs to a whole nudist/naturalist community, so seeing your peers and relatives naked was a norm. As for Ricky and his sister, she grew up seeing her brother already gone through puberty and impressive fit, firm chest, decent sized muscles on arms, filled out and broad shoulders, slender body, long hair enough to cover forehead and ears but kept short in back...biggest thing of all his penis and ball sack, even while limp. From his view, he got to see her grow up from as a toddler to a teenager. Seeing her face mature, her breasts grow to a nice full C cup and a small patch of pubic hair on her pussy mound. Uncontrollably there was times his cock would rise erect and was in her full view from how beautiful her body is. All this creating some sexual tension between them but nothing uncomfortable.
Today was a Friday and nice sunny day, Ricky was making his visit to the parents house mostly to see his little sister. When he got there, she took his hand pulling him to her bedroom and they sat in middle of her bed and began talking about things. Soon out of nowhere, taken off guard she pounced him pushing him on his back and was hovering above him on her all fours, hair cascading down, with full round breasts hanging down only couple feet away from his face. "Another wrestling session, huh?" He smiles saying looking up at her.