Freddi doesn't really have a backstory, he's just a little mouse with a big imagination. He has a special interest in outer-space, the universe, the cosmos, etc., and dreams of being an astronaut when he grows up. He dresses up in an astronaut costume and imagines he's completing missions in space.
His design resembles works of Osamu Tezuka and 60's anime, which was my main inspiration. The color scheme is a reference to Buzz Lightyear from the Toy Story franchise.