User blog comment:B214/Volume 23 discussion blog/@comment-1884090-20170411154430/@comment-29963364-20170411160155

He'll probably make some "big reveal" during the Rias vs. Vali match. Arthur did say that Yuuto Kiba is a "worthy opponent" now that he aquired Gram, the Demon Sword equivalent of Caliburn.

So maybe Yuuto will reveal that he can use Gram safely (maybe for a short time) when he fights Arthur.