Even gods die

What this is about:
It's basically the life of Saiki and his brother, but when they are meant to shadow or teach their new replacement/demigods

my reasoning:
OK OK I may have been a little bit out of my mind when I created this.
OK so let me get you all to go inside of my world view . So I was watching a specific anime.  then I was watching a fanfiction, a crossover fanfiction with Saiki, K and their characters.. 

While watching/reading this fanfiction, I was thinking do you know it would be interesting to  have a world where God's or demigods were sent down to serve humans. And that's what I did now we're here so I decided yeah I'ma do that.

My world building .
OK, so in this world gods, or the strongest God/the god of creation decided to create humans out of his image, and as a way to show respect to that God, other gods had children or demigods, sent down to serve as a servant for humans. To make their lives Easier.

And that's what they did. What did they thought? What if a specific group of humans decide I want to start a war so I will use my demigod a weapon. So whenever a god or a demigod, is created they make sure they have a twin that's not as strong as them, but is meant to kill the demigod if it's ever used in a bad way.
So yeah . But to make sure that the both of them are as pure as can be..
They will be replaced every 100 years.
They are also meant to shadow, and teach their future replacement .

And that's what they basically did but once the replacement is completely ready .
The old guard must die so they have a ceremony and at the end .
Three. Headed creature that looks like the lunarian's from land of the lustrous..
Come and shoot down the old guard/demigod making the new demigod the
New god .

To become a god, there is a lot of rules, but I can't really put them here so I will put it in the first chapter