Sashimi style of stories are sliced along functionality instead of technology. Each sprint, an increment of the work includes more functionality to complete the story. This gradual building of the feature through stories reduces risks, surfaces issues in the design, requirements or misunderstandings early on in the process.
Sashimi is a Japanese word which means pierced body. Basically, it is a Japanese dish which consists of fresh meat or fish, sliced into thin pieces. Each piece is similar in taste when compared with the other pieces.
Sashimi in scrum methodology means every phase of software development cycle in a sprint which includes requirement analysis, planning & design, development, testing, documentation is complete or not and the product is ready to be displayed etc.