Here is the full list of all 13 My Little Sister's Special Place achievements.
Start the game.
Find your little sister in Akihabara.
Go to school with your little sister.
Help your little sister get over her fever.
Start your winter vacation with your little sister.
Enjoy a soak with your little sister.
Share a kiss with your little sister.
Go to the shrine with your little sister.
Make up with your little sister.
Help your little sister practice her swimming.
Care for your sleeping little sister.
Have dinner with the whole family.
Give your heart to your little sister.