Stick an aether generator with no cap on it's power level and let it overload, then drop it into the gas giant. Not something made to release a focused aetheric energy wave, just something not built to build up to that much power and let it break down at random itself. The explosion will probably ignite the gas giant, but the thing is, that'll -still- basically cause it to turn into an expanding cloud rather than, say, a brown dwarf, simply because there's really very little middle ground between those two stages and they are entirely dependent on mass. You can't just pump enough energy into jupiter and get a new star, that's not how stars work. You have to get the core pressure high enough from simple gravity to start nuclear fusion going in a runaway process and that's a matter of mass, matter composition, gravity, and pressure, not just heat.
Igniting a gas giant would, basically, just be setting off a bomb to kill practically everything in that particular solar system depending on how dense the cloud remained when any other planets swung through that area, assuming the sudden change in gravity didn't utterly fuck the orbits of everything involved.
Would this kill the -star-?
No. It wouldn't even explode the planets provided they weren't directly next door. It'd not be something full nova strength, it'd be ranging up to that point, but not that high. Even a star going nova won't actually DUST a planet if the planet isn't close enough or the star isn't dense enough. Blast the atmosphere and a good layer of the crust off, yes, but there'll be a planet still there.
Stars would be destabilized, centuries shaved off their total life span, stellar activity enormously increased, more flares, acting a lot more like a very young star.