In the new "Fairy Tail" chapter, Gray had an awakening of his new stage of power. As such, with Invel failing to calculate this outcome, he has decided to fight using his full strength.
According to the Hall of Fame Magazine, Juvia and Gray were compelled to battle one another in Chapter 499, and they must fight to the death. Of course, Juvia did not want to follow the order to fight Gray, but it was unexpected for a wicked magic to make her do something she finds unacceptable. The same is true with Gray, who feels the power trying to keep him fighting Juvia. As such, despite their best efforts to hold back, the power was just too great and they start fighting.
Invel, in turn, is entertained by their duel, with him placing his bet on Gray prevailing against the water mage. He even went so far as to say that he confidently knows that his calculations will never go astray. As Juvia thinks about how unacceptable it was for her to put Gray in harm's way, she put on a last ditch effort to stop the madness, summoning a water transmuted sword and stabbed herself.
She was not alone in the sentiment, though, since Gray did the same sacrificial act to avoid harming Juvia any further. They then fall into unconsciousness, much to the disbelief of Invel, who cannnot accept the fact that his calculation was wrong and that he never expected Gray to try taking his own life for Juvia's sake.
After Invel leaves the scene, Juvia manages to use her Make Blood magic and transferred her some of her blood to Gray's body. As he opens his eyes, Gray just begs Julia to live, but regardless her eyes stay closed. Regardless, "Fairy Tail" Chapter 500 might show Gray and Invel's fight, with a possibility of Natsu helping him defeat this villain.
