As he walked out of the room, he made a quick decision. "You know... maybe going inside a girl's boobs would be fun? I wonder what it's even like in there.." He kept walking, with the intention of finding a girl outside. Walking past his sister's room, however, he couldn't help but take a peek.
Cracking the door open, he saw his younger sister had fallen asleep at her desk, seemingly while reading a book. "This'll be perfect!" He stepped inside, and closed the door as quietly as he could.
Tip-toeing over, he tried to gauge how hard it might be to get in. After a few seconds, he decided to just go for it, and see what happens. Carefully, he decided to move his sister first, taking a moment to get her on her bed. Once she was secure, he reached down, and lifted the front of her shirt.
He carefully lowered her bra; Seeing her mostly flat chest gave him a small erection, looking at a girl's breasts for the first time. He took in the sight for a few seconds, admiring the small bumps, before deciding to get it over with and get ready to crawl in.
Taking his clothes off, he hid them under her bed, trying to make it hard to find. Then, making sure he had enough space, he crawled up her shirt and up to her breasts. With a deep breath, he pushed his head against it, the top of his head putting pressure on her right breast. With his head in position, he keeps pushing, and hopes it works...