Therefore, even though the Demoniac Realm was just "playing" and not fighting, the fear was that even if they did not ally with the Demon Realm, what if one day they accidentally created a loophole that led to the Demon Realm attacking the Celestial Realm? The Demoniac Realm would definitely not help either side.
Once the war started, the gods of the Celestial Realm were naturally able to withstand it, but the Celestial Realm was not alone; it was also the head of the Lesser Three Realms. After the battle, the vulnerable Mortal Realm and the weak Peaceful Realms would inevitably be involved.
Because neither the Demoniac Realm nor the Demon Realm alone could necessarily take down the Celestial Realm, but their real goal was not to take down the Celestial Realm; they wanted the other two lesser realms.
Thus, an alliance between the Celestial Realm and the Demoniac Realm to suppress the most brutal Demon Realm, keeping the Demon Realm from acting rashly, was the best strategy.