"Gachimuchi" is derived from two Japanese terms: "gacchiri" (がっちり, "muscular", "athletic"), and "muchimuchi" (ムチムチ; "chubby", "throbbing").
On September 30th, 2007, a video clip from Billy Herrington's video, "Workout Muscular Men 3", was uploaded to Nico Nico Douga as a bait-and-switch video, as "Professional-Pants Wrestling" (本格的 ガチムチパンツレスリング, "Honkaku-teki Gachimuchi Pantsu Resuringu"). It nonetheless gained more than 5.5 million views in less than five years, and spawned many musical remixes and comedic edited videos involving him and other characters, under various tags, such as "Gachimuchi Pants Wreslting" (ガチムチ パンツ レスリング), or simply "Wrestling (Series)" (レスリング （シリーズ）), "Forest Fairy" (森の妖精, Mori no Yousei) and "Philosophy" (哲学, Tetsugaku).
It was also used by the Swedish Hearthstone gamer, Forsen, in some of his videos and in his Twitch account, in which he sometimes speaks and messages to Billy Herrington on Twitter.
- Gachimuchi is also a name for a subgenre of "boys love" or "bara" (薔薇, "rose"), an art or fiction genre involving homosexual characters. Among English-speaking fans of the subgenre, it is referred simply as "bara".
- As much of the sources for Gachimuchi were from gay pornography videos, many scenes in the videos had to be cut or censored, to comply with the rules of the websites that these videos are being posted in.