Leash breaking your puppy takes patience. Shibas, being independent and stubborn, can sometimes object to being restrained by a collar and leash. A harness as the one in the video, gives them freedom of movement, and also limits chances of them slipping out and escaping. As in all aspects of training your puppy, the sooner the better.
Take your puppy to a large field and let your puppy walk where they would like. As they become accustomed to being on a leash, slowly tug them in your direction. This slow approach and treats will entice them to see things your way.
The harness on the video fits well but not too snug. It is also lightweight and not too restrictive.