Streaming, now the dominant format for music consumption, has fundamentally altered musics role in daily life. With platforms encouraging users to engage with music as a tool for mood regulation and activity enhancement through curated playlists and streams, this shift has created whit might be termed a functional turn in music. However, not all music is created with a specific function in mind, leading to the appropriation and repackaging of existing genres for functional purposes. Despite this growing trend, the broader effects of this transformation on the musical practices of listening, production, and curation remain under-explored. FUNCTUMUS addresses this gap by investigating the functional appropriation of music through a case study of lofi hiphop (LFHH). Originating in the early 2000s, LFHH was rebranded in the 2010s as music to relax/study to by online curators, and the rhythms, grooves, and compositional structures of subsequent LFHH have evidently adapted to fit this new functional role. The functional appropriation has also reshaped practices of listening, production, and curation associated with the genre, causing friction between its functional and creative dimensions. FUNCTUMUS builds on these observations to examine the functional appropriation of LFHH from the perspectives of listeners, producers, and curators, whilst also accounting for its cognitive-behavioural effects and the hegemonic systems of power and in which it is embedded. The study employs Netnographic observation of online communities central to LFHH and qualitative interviews with listeners, producers, and curators, supported by musical analysis. A unique theoretical framework, drawing from Musicology, Sociology, and Semiotics, underpins the research, offering a comprehensive exploration of how digital streaming reshapes the form and function of contemporary music.