I'm trying to create a scenario where the local star is "quickly" (suddenly up to thousands of years) removed, dimmed with reduced output, destroyed (maybe), or otherwise fundamentally changed as to have dramatic ramifications on all life. Keeping the local system in orbit would be ideal, so complete destruction scenarios may not be the best fits.

The biggest challenge I'm having is that the only star-harvesting ideas I know of are variants Dyson concepts, which seem to commonly seek to harvest the energy of a star throughout it's entire/most natural life (implying that this is the most efficient method, which I am guessing makes sense but I don't honestly know). Dyson shells are suboptimal because they can be interrupted by an intelligent outsider leading to the potential to simply "rescue" the star, but more importantly my understanding is that a shell variant would generally be ~1AU in scale for efficiency-sake, making it disruptive to the type of story-telling I'm looking for -- it would either enclose or be obscenely close to most earth-like planets unless I'm mistaken.

Because of this, I'm struggling to think of ways and motivations for an alien or other being to quickly disrupt the local star. I'm looking to avoid scenarios where the star is simply destroyed for the sake of it's destruction, but rather where it is used for a logical purpose by an uncaring 3rd party.