This is usually used, when a character gets transformed into a robot, or just basically becomes a machine version of themselves. It also counts, and this is the case for most stories featured here, is when a person wears something that makes them appear / behave like a robot. Everything that features, like a robot suit or something, is part of this here as well.
Ma1d Theft Protection by Ary0901
The first entry in the amazing Ma1d series by Ary0901. Ma1d Theft Protection by Ary0901 Pixiv The first of manny Ma1d stories