Tongari Boushi no Memole

Memoru is one of 245 people who came to earth from the Riruru Star when their ship had an emergency crash-landing on earth. Memoru's people have such tiny bodies that they could stand on a human's palm. One day she hears lovely music, and she follows its source and comes upon a huge house she hasn't seen before to find a girl taller than her playing on the piano. Memoru visited her again secretly with her friends Popitu, Rupangu, and Pi, but the human girl, Marielle, seemed sick and likely to die any moment. Feeling sad for the girl, Memoru's tear drops on the girl's lips. The girl gets better and a strong friendship starts between them. Marielle meets a boy named Oscar and falls in love with him. The three become best friends, but Grace, Oscar's mean girlfriend, tries to find out the truth about Memoru, putting Memoru's people in danger. In the end, Grace helps Marielle and Oscar get Memoru's people back to Riruru Star, but Memoru stays behind on earth.

(Source: Anime News Network)