Star (スター, Sutā) is a special chapter included with Volume 13.
Sweet Mask is performing at his concert tour his latest album, when the concert stadium was suddenly attacked by monsters from the Monster Association. The monsters attack Sweet Mask during his concert and while his fans were frightened, Sweet Mask simply continues his performance.
The audience wonders if this is part of the show. While the monsters try to attack Sweet Mask, he merely taunts them and in the end finishes them off with little effort. After the concert, the staff comments that the concert was an incredible success despite the monster attack. Sweet Mask is seen back stage and he decides to investigate the Monster Association.