
I read some spoilers, not the novel; but why would he keep the gun? Is it to torture himself with the memories, I kinda hope so.
On a totally random note If that is the case, keeping a gun in the house seems a bit like tempting fate. I didn't think it was that hard to buy bullets vs if he kept bullets in the house as a memento, it would be safer because it's much more difficult to purchase a gun.

spoilers for the gun
the gun was a gift to kwon ido from his grandfather i believe, and in the first life, he kept it loaded with the original bullets that came with it gifted, and it was this gun jeong sejin used in front of him, and later kwon ido would too. so in the next life, kwon ido kept the gun without the bullets as constant reminder of his mistreatment to sejin in the first life, and hence to never repeat those same things ever again in this second chance.

Well, just to keep it fair, without spreading stereotypes, I live in america, and that has never been a tradition of anyone I know. There are some places in the south like that, I'm sure :) But it's certainly not an american tradition. just to keep things real and open minded about different peoples of the world:)
this is their second life. give the ML a fucking chance to redeem— it's literally the purpose of this story