Otonari-san wa Inkyappoi no ni Kakure Bitch

Daichi-san is my neighbor who I secretly have a crush on. She has absolutely no interest in fashion and so she's kind of plain, but even through her clothes you can tell she's incredibly busty...

One day, a pair of women's underwear fell onto my balcony. I had a hunch about where it came from, and when I tried to peep next door through the balcony, I saw Daichi-san masturbating! I knew I shouldn't be watching, but my hand on my penis wouldn't stop moving...

Just as I ejaculated on her panties in my hand, my intercom rang!! I opened the door, and standing right there was...

(Source: Melonbooks, translated)

Note: Released at Comiket 99.