Shakui was conducted when an official was given an assignment which should be performed by higher-ranking officials, and in some cases he was formally promoted to that higher rank if he succeeded in the assignment.
本来の位階よりも高い位階が担当すべき任務を命ぜられた場合に行われ、その任務の成果次第によってはその位階が正式に叙せられる場合があった。