The origin of Chashu came from Chinese barbecued pork called  Char Siu( 叉烧  )

Traditionally, Chinese Char Siu is marinated in soy sauce,honey,hoisin sauce,rice wine,spicy powder. The meat is then either slow roasted in a covered oven or barbecued over a fire. 

Seared Chashu
Kopan Ramen Soup Menu with Chashu

 Ramen soup with chashu

Ramen soup & Chashu slice

Ramen soup & Chashu  and with egg