User blog comment:B214/Volume 23 discussion blog/@comment-1884090-20170411154430/@comment-10330822-20170412032104

Well, the problem with that is that we don't know if Gram and the other demon swords can fuse with Sacred Gears like that. After all, demon swords aren't the same as holy swords, and Ascalon was specifically altered so Issei could use it.

Also, I feel if Gram and the other swords are fused together, it would be like an Excalibur pieces deal, but that's not quite what's going on. The Excalibur pieces were originally the same, and the pieces needed to be taken to Heaven so they could be specially crafted into Ex-Durandal, which had the ability to split into True Excalibur and Durandal later on.

However, Gram and the other swords are each their own seperate sword, fusing them together would be like fusing Excalibur, Durandal, Ascalon, and Caliburn together.

No, I have a feeling he'll just dominate the swords with his demonic energy, completely removing the threat of them taking his life force from the equation entirely. After all, this isn't the first time demon swords have appeared in a series. Usually, the demon sword will have its own will, and will actively devour or hurt a weaker being that tries to use it, but if Kiba proves to be dominant, the sword will obey him willingly.

As for Kiba's sacred gears, the fact the holy demonic sword can absorb holy energy and make it demonic, or take demonic energy and make it holy, if very threatening, especially since if he merges it with Glory Drag Trooper, and gives each one of his dragon knights a holy demonic sword, he'll already been a serious threat.

I could imagine a fight with Issei, where Kiba is wearing his dragon knight armor and wielding Gram and maybe Nothung, and attacking Issei while his dragon knights steal the demonic energy from Issei's body to attack him with holy energy. That, along with Gram's dragon slaying abilities, would be very dangerous. Hell, Issei could even use Ascalon properly because the holy demonic swords would steal its holy energy to empower demonic energy in themselves.