Do drills for different situations on each day of the week.
The positions for Star Pieces distributed as rewards will vary depending on the day.
Each day will have 4 difficulties, and you can acquire more valuable Star Pieces by completing drills on higher difficulties.
You can only acquire a set number of rewards across all difficulties in Situation Drills.
Take the difficulty level into consideration when doing the Situation Drills to maximize the amount of Star Pieces you can acquire.