"Goth" is a subculture that originated in the punk and heavy metal scenes in the UK and the US in the late 1970s and early 1980s. It's characterized by a dark, mysterious aesthetic, often involving black clothing, white makeup around the eyes, and sometimes elaborate costumes or accessories.
"Imouto" is Japanese for "younger sister." In anime and manga culture, it's used to denote a character that is portrayed as a younger sister figure, often with a more innocent, childlike demeanor despite possibly being an adult.
Combining these two terms gives us the tag "GothImouto," which would likely describe content featuring a Goth-styled character who is portrayed as a younger sister or has a younger sister figure in the scene. This could involve a relationship between the characters, or simply be a description of one character's appearance or style.