User blog comment:B214/Volume 23 discussion blog/@comment-1884090-20170411154430/@comment-10330822-20170412033559

I feel for most anime sword/weapon users, if you aren't controlling the sword, it is controlling you. Cao Cao, who is a master at the use of his True Longinus, probably understands this better than anyone.

Gram showed during the battle with Siegfried that it respected Kiba more than Sieg, hence why it abandoned Sieg for Kiba. However, while it might view Kiba as more powerful than Sieg, it may not see Kiba as stronger than itself. As a result, Kiba hasn't gained the full respect of Gram and thus it still absorbs life, even though it prefers Kiba to Sieg.

So, naturally the next step is to prove to Gram and the other swords that he is dominant. This is very amusing to be because Kiba's ability to generate swords makes him "similar" to one, almost like he is a demon sword, and he needs to prove he is the Alpha.

Personally, I feel this is why the Siegfried Institute couldn't perfectly duplicate the original Siegfried's condition who apparently could use Gram. The problem isn't in the genetics, its a question of instinct and dominance. Siegfried could use Gram so effectively because he earned Gram's respect, granted its also possible the original Siegfried lost life force to Gram, but only because he wasn't as strong as Kiba is/will be.