Once upon a time, An alien tribe lived in a parallel universe with the same appearance and attitude as humans. It's not like they're evil or good, just naughty guys who like to mess with people. However, there is a big difference between humans and these creatures which is that they can sneak out of all parallel universes and galaxies to steal whatever they want. This is the reason why suddenly, in our world, something has been lost, someone has died, a relationship has crumbled, etc.

They are known as the Secret Thieves! In spite of the pain of losing our beloved ones or things, we are unaware that they have been stolen from us just for fun. Yet we cannot see or stop them! Therefore, the best thing we can do is not take anything too seriously. This is because eventually, The Secret Thieves are gonna rob them off us and all thing will remain is pain.