A White Star.

It will take power of a Celestial or an Origin god to breach the defense. After all, they are made of materials that can withstand the explosion of a real star not some star wannabe. 

Legion-5 held on in the face of the all-burning flames. He even kept punching Devoni. The two of them struggled in the air as Devoni tried to pull away. But Legion didn't let him go. He even grabbed the grand god's neck.

Then he said, "My turn."

That's the first thing he has said to the grand god of fire who has come to pay him a visit. It is also the last thing that Devoni will ever hear. 

Legion-5 opened his mouth then. In it is a white super-compressed ball of energy. The surrounding air became charged immediately. Even the fire started to create sparks.

The grand god roared in fear, "Noooooooo!"