This conference paper presents a segment of ongoing doctoral artistic research titled "MONSTER SINGS," focusing on the liminal positioning of the opera prompter’s voice. The research explores the prompter’s vocal presence as a phenomenon perpetually suspended between public and private, silence and sonority, and being voiced and unvoiced. The author, drawing on his dual experience as a professional opera prompter and a transgender man, investigates the "prompter’s box" as a space of transition. The contribution frames the act of prompting—required to be perceptible to the singer yet undetectable to the audience—as a methodological tool for (re)constructing and rehearsing the trans* voice. By analyzing the "untraceable" nature of the prompter’s cues, the text inquires into the (im)possibilities of being heard and the erotics of vocal "leakage" in the operatic machine. Through the lens of "monster theory" (referencing Paul B. Preciado) and queer performativity, the paper proposes that the prompter’s voice does not merely assist the singer but forms a dialogical partnership that challenges the boundaries of individual identity. The work concludes by reimagining the "void" of the prompt corner not as a site of erasure, but as a fertile ground for new forms of "trans* voicing" and relationality.