Thanks for the new chapter!
"Survival of the fittest" technically is the main concept of Kodoku - to make the best one rise to the top.
Though I have to say, pitting poisonous creatures against each other is just creating the scenario of the 'frog in a small pond'.
The one who survives the kodoku might be the best amongst those it defeated but once that 'top creature' gets out of the kodoku/basket, it doesn't mean it will be the strongest within the outside world.
Even the most venomous cobra can be killed and eaten by a non-venomous/poisonous creature like the mongoose after all.