These are two of my O.Cs for a manga I have in mind called 99 manga.
One of the girls is Terra her power is the power of life. She can heal you or bring you back to life. But she has a big temper and will nearly beat you to death and then revive you so she can just do it over again.

The second girl is Jade.
She has the power of death and her power spreads like a disease. She can't control how fast or far her power travels so her twin terra reflects her power with her own.
When ever they are around each other there powers are ineffective.
Jade has a temper but not as bad as terra though she will sit there and watch you get beaten half todeath.