Mouhitori no Watashi

On a hill in a wealthy residential neighbourhood, with kind parents and plenty of good friends, the cheerful girl Kahoko, nicknamed "Kako," lives happily. One day, due to the sudden death of her father, that life completely changes. A beautiful girl named Naoko moves into Kako's old house, and Kako's heart is filled with trouble. Naoko lives with a little secret that she doesn't want anybody to know. But Kako stumbles onto Naoko's secret by accident, and afraid that Naoko might steal the heart of Kako's first-love Noboru. So Kako, in front of Noboru... tries to reveal Naoko's secret... This is the story of how a girl grows up, surprised and perplexed, with budding jealousy and envy in a complex struggle of the heart. ( MangaUpdates )