Mukuronaru hoshi

The story could basically be split into two halves. The main story is about Tamai Shiina, who is an energetic middle-school teenage girl. She visits her grandparent's over the summer where she runs into a very strange creature. Shiina has had lots of strange dreams as of late and also when she was younger, and this strange creature is somewhat related to her visions. She names the small cuddly star-shaped creature, Hoshimaru.