Board Thread:Rebirth: Applications/@comment-26116209-20141009164453/@comment-26116209-20141014085320

One of the disadvantages were that if the seal was being used too long, it could cause a lot of pain and damage to her body. Knowing this, she tries to never use the seal that long, only if truly necessary. That way, the Shinigami isn't able to take over.

The curse seal gives the abilities that are listed because the Shinigami practically is giving part of himself through the seal, as the user gains an appearance that matches his. Therefore, they would gain those abilities since that is what he is capable of.