Complete all routes with at least one ending. Then, start a new game and select the "Fulfill the promise" option.
The following birds prefer the listed beans.
Complete the BBL special story after unlocking all previous endings.
Perform the indicated tasks on the listed dates. Attend gym every day instead of studying music or math to raise your Vitality stat as high as possible.
Save the game, as each achievement or trophy requires a different path at this point.
Do not romance anyone. One such way is to follow Okosan's or Yuuya's route until the end, then deciding not to go with him.