Moreover, for the world itself, this kind of fusion isn't a good thing at the beginning.
It seems like a complementary balance, but in fact, during this process of balance, the world itself becomes vulnerable, and the original framework of the world is altered due to this complementarity.
This prolonged change, as long as it isn't stabilized, keeps this vulnerability from disappearing.
One could say that the world seems stronger from this complementarity, but it has also become weaker, much like a monster entering a rampage mode: strength increases, but the damage the monster receives is also greatly increased.
Monsters that were originally difficult to one-shot kill might now be possible to kill instantly under these circumstances.