Complex sentence: When he realizes the true threat that Demon Card are to the world, he then promised Shiba that he will complete the collection of Rave and defeat evil and end all of it and sets off to find the pieces of Rave to restore peace to the world.
Split into simpler sentences: When he realizes the true threat that Demon Card are to the world, he then promised Shiba that he will complete the collection of Rave and end all of Demon Card's evil. He then sets off to find the pieces of Rave to restore peace to the world.