A pair of non-identical twins Akari and Kurayami have the opposing demons of light and dark sealed inside their bodies. As you can see Akari has the seal on her arm, giving her incredible strength in that arm along with the ability to kill people by expelling a dark shadowy mass from that hand that eats flesh like acid. Kurayami has the tattoo on her shoulder blade in this picture but I've since moved it to the palm of her left hand so she can heal people with her touch and expel bolts of concentrated light-energy. Ironically the words Akari and Kurayami mean light and dark in japanese, Akari (light) has the dark demon sealed in her arm and Kurayami (dark) has the light demon in her arm. Yay for pointless confusing irony. The scroll says Twin Sisters on the side in front of Kura (short hair, pupil-less eyes) and Twin Demons on the side behind Akari (long hair, cat slit eyes) in japanese.