I think you have the start of a wonderful idea. I love the character sketch and like the idea of a "Guardian of Hope" It's really unique and I feel if you continue with this, that it would become a great inspiration piece to all audiences. Although I would be careful to not fall into an overused theme of schoolgirl who finds she has secret powers and wishes that she had her ordinary life back. I'm not sure what your plot is yet but you should definitely build your story to some climatic effect...I feel like your character Christina should be burdened a little each time she changes someone's life, because to be a "Keeper" of something you have to invest alot of yourself into that role, so after awhile it should begin to wear on the bearer's soul. Just some suggestions, I am excited to see where you take this! She's very cute! Although I'd love to see her in color, even though the grayscale is great in itself. Anyway, I hope this helps. =3 And good luck!
~Rin XD