Can someone help me with the name of this anime? all i remember is that stars were involved...?

okay so from what i remember there was this girl who went somewhere with her family i think and she went swimming found this alien star or whatever. im sorry i dont remember much but i know there was this battle betweeen the star things. her star looked like a normal yellow star cept it walked had eyes....yaknow the works. and i know the girls friend had one too and she had to kill her at the end. someone please help me. i know the details are vague but please try T.T