Within the creative Undertale fandom, the term "Bad Brother" is strongly linked to an alternate universe (AU) with a dark premise.

Progressing smoothly through the saga requires precision. Missing a single event during the in-game morning cycle can lock you out of evening story rewards. 1. Master the Daily Routine

To help others who might be looking for the same thing, could you share a bit more about the "Bad Brother Saga" you have in mind? Knowing whether it’s a game, a show, a book, or a fan story can help you get the most accurate results.

However, because it specifically focuses on Link’s silence as complicity — the brother isn’t possessing Link; Link simply follows orders without hesitation.