satoshi hiwatariSatoshi is the ‘host’ of Krad. As the host, Satoshi is usually the active one who controls the body the most. Krad rarely ever attains control, but when he does he uses the body most of the time to attack Dark or Daisuke (whoever was the one that pissed him off.) Almost 100% of the time, Satoshi is actually the one who forces Krad to be dormant In the body while he regains control.
When Krad takes over Satoshi’s body he tends to use great amounts of magic. This is a problem. Though small amounts of magic would not effect Satoshi very much, Krad insists on using as much as he can to destroy whoever pissed him off. He always has his wings out, which also require magic. The more magic Krad uses, the more Satoshi has to suffer once Krad goes dormant. Satoshi is almost always left in a very tired and pained state.
Krad does know that he is hurting Satoshi, we know this because in one chapter he states that his host (Satoshi) is almost at his ‘limit’. So why does Krad keep leaving Satoshi in that sorry state? Because he’s trying to achieve something. It is obviously something so important to him, that he does not care what state his host is left in, as long as the host is alive.
Krads relationship with Satoshi could probably be called parasitic, depending on how you look at it. So needless to say, their relationship is not a good one. Satoshi rarely ever speaks of Krad, so it is unsure what he thinks of him. But I think that it is probably very safe to assume that Satoshi hates Krad and wants him gone.
But Krad on the other hand, does speak of Satoshi. Krad tells Satoshi that he is ‘his everything.’ It is unsure if Krad really thinks of Satoshi as the most important person in his world, or if he just says such things as a form of manipulation. It seems to me that Krad does want to maintain some sort of relationship with Satoshi, while Krad is out in a recent chapter Krad claims to be ‘protecting’ Satoshi as he destroys a piece of artwork, then proceeds to try and kill Daisuke.
From what I gather, I think that Krad definitely does care about Satoshi. But keeping him healthy is pretty low on his priority list. He probably get really irritated with Satoshi, since he is never released of both of their wills.
Recent chapters have shown an interesting development in the twos relationship. Satoshi calls forth Krad to save Risa Harada from falling to her death. There is a interesting possibility that Satoshi did not use the ring to call forth Krad, and that Satoshi's feelings for Risa called forth the change. Satoshi then used the ring to suppress Krad after Risa was safe. It is very questionable about if it was Krad or Satoshi which actually saved Risa (although i do not think it is a question of whose will it was.), but it's possible that Krad was the one who physically did the saving. The somewhat confused words he gave to Risa would then be explained. If this is the case, then both Krad and Satoshi were probably both extremely confused. Krad, who would normally force his way out through anger and hatred would have been called out as a result of Satoshi's feelings. This would be huge, and could possibly lead to a more stable relationship between the two.