Even though Leo could block a legend-grade attack using his bloodline [Fake Immortal God's Bloodline], the Fire Void Dragon King didn't release all the [Flaming Void Missiles] at once; instead, he released them with some time gap.
Hence, it would be useless for Leo to block all the incoming [Flaming Void Missiles]. Therefore, he chose to sacrifice his arm to raise the potential of the [Nether Rage Booster].
'I can regenerate my arm after the special effect [Regeneration] comes out of the cooldown.'
This was the thought in Leo's head when he sacrificed his arm.
However, to regenerate a new arm, Leo had to wait for another 12 hours and until then, Leo thought it wouldn't be a problem for him to survive in this Grade Void Dragon World.
"Since the [Flaming Void Missiles] are taken care of, it's time to take care of the Fire Void Dragon King."