It Starts from the Inside

Sho Itoguchi, an office worker who runs a site selling urethra bougies as a hobby, finds his boss's name, Noriyuki Kiyama, within the list of prospective buyers. Later on, he brings some urethra bougies to Noriyuki's home and starts his "lecture" just like that. Despite it being Noriyuki's first time, he's drowning in pleasure in front of Sho. Sho can't hold back his excitement...!

(Source: Renta!)

Note: Includes an extra chapter.