The Stainless Boy (ステンレスボーイ) is a robot.
There is a new Yorozuya in town therefore Gin, Shinpachi and Kagura are heading out to shut them down. On the way there, they meet several people who praise the new Yorozuya. Hearing this, they dash into the office and it happens that the members of the new Yorozuya are the predecessor of Kagura and Shinpachi.
Gintoki learns of another Yorozuya, seeing that they have a website they go to check it out. The members of this Yorozuya are similar to them. They then raid their headquarters. And find three people and something like a robot.