Uchuu Kyoudai: Itten no Hikari
Japanese title: プラネタリウム 宇宙兄弟 ～一点のひかり～
Type: Movie
Episodes: 1
Source: Original
Genres: Comedy, Sci-Fi, Slice of Life
Studios: A-1 Pictures
Producers: Digital Media Lab
Duration: 38 min
Rating: PG-13 - Teens 13 or older

The anime's original story features Mutta and Hibito during one summer when they were children. During the summer when Mutta and Hibito made their promise to go to space, they met a young girl who also had a wish.

(Source: ANN)