Haruna is the Shield of Messiah which is to protect the Messiah. She first asked Shinya to meet her at the roof of the school. Later when she gave him the Guide To Salvation and he was unable to read it she begins crying thinking that she made a mistake. When Shinya saves the book and bring it back to her Shinya got chosen by the book to become the Messiah. She was good friends with Lilu the Princess of Ruin but that was shattered with Haruna unable to help Lilu when she was dragged off by the Prophets acolyte to initiate her to become the Princess of Ruin. Haruna is in love with Shinya but cannot fully express it because she is dying. Harunas power is in healing the direct opposite of the Princess of Ruins power which is to destroy. She can heal almost any lethal wound but that comes with a drastic feedback. Her life force is shortening for every time she uses magic. She is dying from excessive use of magic. Shinya is meeting the ruler of New Celestia who has the same power as Haruna. Currently the new ruler sent out Haruna in her weakened state to find Xeon the Lion Lord because Shinya wont join New Celestias side. He is the only one that can heal Haruna. The Prophet Vaul who was Harunas guardian could possess her body and do physical activities relay message and even control her. He one time possessed her body and created time rips to destroy the Earth but failed due to Shinyas love for her and her strong will with the help from Lilu. When she was the Priestess of Oblivion she was able to use destruction magic with no strain to her body we dont know if that was due to Vauls combined strength. But if she uses destruction magic Haruna is in par with the Princess of Ruin but will strain her body. Source: Wikipedia