There is a lot of ways to get the Destruction 4 achievement, but many of them require some amount of luck to find the right gear and enemy combination.
This method requires you to only re-roll the starting room and depending on your luck, it can take longer, but after getting the right starting room it is 100% consistent.

Start with Naqui as the Culture and Secutor as the Class.
God does not matter as long as it does not accidentally kill enemies for you.
For stats I chose Strength, but it does not really matter that much.
For skills, with the first 10 points pick Life Chant and Frenzied Chant.
You should get enough points during the process to pick another level for Frenzied Chant.


You need to roll a starting room where one of the enemies is a Rat-man Peltast


You need to clear the room until only a single Rat-man Peltast remains.
You should position yourself next to the rat or at least close, to not lose Poise to movement.
Then you can put a weight on your space bar for around 15 minutes and slap the rat for millions of damage.

The basic idea in many Destruction 4 guides is to build damage by infinitely stacking some effects that increases your Hit, such as Inflame.
The issue in getting to a point where you can stack effects infinitely is that usually it requires some specific gear.

For example, infinitely stacking Inflame only works consistently when you have the Gold Plating chest armor, since you have always at least 0.1% chance to lose half of your stacks, because Inflame loses half stacks on taking damage, Block chance is capped at 90% and Dodge has always minimum 10% chance to fail, and Shrug Off from Armor also has a minimum 10% chance to fail.
You also lose one of each effect stack at the end of a turn, unless you have some gear or skill that states otherwise.

But with this setup, you can stack Attune, Poise and Anoint infinitely, with stacking Inflame on the side to speed up the process.
All of theses effects increase your Hit.

Naqui gives you Attune stacks on being attacked and the Rat-man Peltast will attack you multiple times in a single turn, guaranteeing that you get more stacks than you lose at the end of the turn.

Secutor gives you a random martial effect every game turn, with the amount being equal to your highest stat. This effect can be Poise, Anoint, Inflame or Evasion.
For our purpose Evasion is useless, but getting 6 or more stacks at a time basically guarantees that you will get more Poise and Anoint than you will lose at the end of the turn.
You can choose to spend all your stats on Dexterity to get the highest effect stacks from Secutor, since with my starting setup Dexterity is the highest stat, but you can optimize your starting stats also by picking a different god.

Picking Frenzied Chant as a skill increases the amount of Inflame you get every game turn.

Picking Life Chant offsets the self-damage you take from Frenzied Chant as well as any damage that the rat occasionally gets through our defenses.

When clearing the room of other enemies, you should get enough points for a second level of Frenzied Chant.

After the room is cleared of all other enemies except one Rat-man Peltast, you can sit next to it pressing stand still until you have enough stacks to reach the 1 million damage mark.
You will occasionally lose half of the Inflame stacks for the reasons stated above, but you should be getting infinite Attune stacks and unless you are the unluckiest person in the world and only get Evasion from Secutor, you should also build infinite Poise and Anoint stacks.
In theory you only need Attune and the other effects simply speed up the process.

I don't know how to calculate the damage based on stats, so I went a little too far and got 43+ million damage. You can try to ballpark the required stacks based on my results.