God fire is the very flame created from a god spark when someone becomes a god. It burns almost everything apart from the god that it belongs to. Even a vessel that is attuned to that god is not safe from it. A god needs it to convert faith to divine energy so it is very important to a god. It can be said to be the foundation of their faith.
Using the god fire on things apart from faith energy will deplete it until it dies off because only faith can fuel it. Using it on a god's vessel will quicken the rate at which the vessel deteriorates and dies. It will also weaken the god. That's why the Celestial was holding back on using his full power from the start.
He didn't go all out when the battle started. It would have been a waste of both god fire and vessel if his full power wasn't needed. It is a good decision too since his full power shouldn't be needed for a king of law. But who would have thought that the limit of the estimation of Helios's power is not the limit and that he would fool them?
Holding back made the first vessel unprepared for the sudden onslaught of attack. The Colossus stumbled and began to fall as it lost its limbs. It still struggled to fight back. A fight has not ended until death so the Celestial Supreme increased the power of the god-fire to the level of a grand god. If the power of a high god cannot stop Helios's attacks, surely the power of a grand god should be able to.
The Celestial Supreme still held back from using its full power. There is no indication that it needs its full power. It might be that its inexperience with fighting a king of fire is what's causing the poor showing. He created stronger shields with the power of a grand god to block incoming projectiles. That still wasn't enough.
The javelins penetrated the shields again. They struck the Colossus on the head and torso spreading fire all over it. The Colossus died before reaching the ground. It went out in flames after taking several hits of the javelins of fire.
The other nine transcendents were inwardly shocked by the quick death of their comrade but they didn't show it. The Celestial Supreme controlling them has a strong hold on their emotions and behavior. Instead of being slack-jawed, they used the time that their comrade bought for them with his life to get into formation.
7 behemoths took the vanguard and the remaining two Colossi in the group reduced their heights to match the behemoths and followed along. The behemoths didn't care for shields as they ran toward Helios without worry. They can't create shields so they have to rely on their armor. Their armor has not disappointed them so far so they are confident of its defense.
The javelins of fire impacted the hard body armor and exploded but the Behemoths were unharmed. They ran through the explosion as if they are taking flame showers. The combination of their armor and the divine power of a grand god protected them from Helios's fiery wrath.
Their formation held up under the assault of the javelins. None of the javelins could get past their impenetrable defenses which left the Colossi behind them safe from harm. That was until the spears began moving erratically. They stopped moving in straight lines and instead swerved around the behemoths to bombard the Colossi behind them.
"Move on." The Celestial Supreme decided.
They had two options, slow down to defend the two Colossi or continue forward to stop Helios from trying to stall them. The Celestial Supreme can sense a terrible power brewing within Helios and he chose to prioritize it over the safety of the two Colossi.
The two Colossi defended themselves against the bombardment by creating shields at the level of a Celestial. Their shields blocked all the attacks keeping them sound and safe. They followed behind the Behemoths without any issues until they began to slow down. Their speed dropped as they weakened. Then they died after defending numerous waves of attack.
They became too weak to put up their defended and were struck down but it wasn't Helios that killed them. The burden of using the power of a Celestial finally got to them and they were consumed by the God fire that previously protected them. Helios only provided the reason for them to be condemned to a painful death of having their body and soul consumed by the fire of a god.
The Celestial Supreme's decision to sacrifice the Colossi was the right one but it changes nothing. Helios specifically targeted the Colossi in their group because they can enlarge while Behemoths with incomparable defense can't enlarge. A colossus would have been able to reach him quickly if they are allowed to use the advantage of their size.
The lack of defense of the Colossi made them vulnerable to the javelins and made them great targets. It also kept them at bay and gave Helios time to do what he wanted. He started attacking them at a great distance away so he was ready for his full attack by the time the strong Behemoths could get close.
Helios grinned as saw the 7 intact behemoths coming for him. His divine sense whispered to them, "Playtime is over."
He has been preparing something within the barrel that he combined two of his arms to form. He fired it now and the world became dark immediately as the Authority of the Celestial god of the sun was used. The light of the world disappeared because the power of the sun entering the plane has been funneled into Helios. The stolen light was then pumped into the barrel.
The power of the sun isn't being used to power the attack that is to come but to ignite the attack. The attack is powerful enough without the power of the sun, it just needs something to get it moving. Like a little push to make a boulder roll down a mountain. All that power is just for the little push.