Demon king didn't play chess with Deon's life tho ... He just had a bet on his survival. The other person with purple hair who forced Deon to go to the war is at fault. Demon king wasn't directly involved with Deon's trauma , demon king did bet on Deon that Deon would survive and nothing more nothing less.
The bet was made prior to Deon being sent to war , yes he is directly responsible for what happened, and he only saw it as a fun bet when it cost Deon everything. Demon king deserved to die and Deon was valid to snap after finally realising the shit those in power put him through literally just for their own amusement.
I'm not saying Demon king is not entirely at fault but no , Deon was sent to war even before Demon king knew any of these. If you don't remember go read that again. Purple haired guy sent Deon at war and then brought that bet for Demon king so that he would find it interesting. Maybe Demon king deserves to be punished for using Deon's life as his entertainment. But I'm biased that I don't wanna have him dead. He was from the very first episode of this manhwa , I love him

Bro I liked this manhwa before when Deon wasn't using all his time killing everyone. All he does is killing everyone. I'm tired of this.
It could have an amazing plot without killing everyone , I give up on this manhwa bye.