As it was breaking the limits of the body and using the powers that their body couldn't accommodate, it destroyed their body.
Using Overdrive was like drinking poison that didn't have a cure. This was one of the main reasons as to why people avoided using Overdrive until they had no other option.
It was said that only the person who had a death wish used this since the death from it wasn't ordinary either. It was the most painful death they could have.
Moreover, they couldn't even use Overdrive for more than a minute. Anyone who used Overdrive died in less than a minute.
So it was nothing more than burning your life to use a minute of power as a last-ditch effort. It was useless if the enemy just avoided the attacks for a minute as the person who used it was going to die on their own.
That's why Kellian had told Yaliza to leave. He believed Yaliza needed to stay away. As for him, he could easily escape as well.
