English ver.(Cp. 2) https://batotoo.com/title/19731-hajimari-wa-naka-kara
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...!
趣味で尿道ブジーの通販サイトを営んでいるサラリーマンの糸口は、購入希望者の中に上司である基山の名前を発見する。後日、基山の自宅へ尿道ブジーを持参し、そのまま”レクチャー”を開始。初めてにも関わらず、とろとろに蕩けてしまった基山を目の前にして、糸口は昂ぶりを抑えきれずに…!?