@Stalkerman As much as i agree with you, but sadly, those "things" are immortal.
Take Kyubei for example. There are multiple of it, and just killing one won't end it.
We could also take those from a more light hearted one like a precure. Those "fairies" are soo durable, that even after they (supposedly) die because of the bad guy plan, somehow they come back to life at the end of the fight. The only way for them to "die" is from their natural lifespan or some specific way
They are like energy, can't be erased or destroyed. They could only be converted