Sonic Sonic is a fictional character from the anime series Kekkai Sensen, also known as Blood Blockade Battlefront. Sonic is a unique, intelligent monkey who serves as the loyal pet and companion of Leonardo Watch, the series' protagonist. With his remarkable speed and agility, Sonic aids Leonardo in various situations throughout the series. His mischievous yet endearing personality adds a layer of charm to the series, often providing comic relief while also playing a crucial role in key moments of the story.