1. That's personalized decoration. Some things on Ba Shen's body are decorations with certain meanings, such as the emblem' Moon Wheel' painted in the middle of the back of the coat representing the Ba Shen family, and some personalized decorations representing Ba Shen's bohemian and chic, such as: peculiar red-red unique hairstyle, red belt between his legs, collar around his neck ... plus personality movements and lines, Iori Yagami
There are two possibilities for the second question.
(1) After many times of practice, he gradually got used to this bondage, so he won't fall or make a move in actual combat.
(2) The belt on his trousers is very long, just like nothing, so his legs can be used flexibly.