Here is the full list of all 19 Love n Dream: Virtual Happiness achievements.
You unlock all character information
Maximum 5 impression level for Lucky_Star
Collect total 45 stars
Use Lucky_Star skill 5 times
Maximum 5 impression level for Fiona_23
Use Fiona_23 skill 5 times
Collect all items
Maximum 5 impression level for white_Fox
Maxium 5 impression level for _Valerie_
Use _Valerie_ skill 5 times
Spend 6000 gold or more
Trigger evasion white_Fox passive skill 5 times
Collect 20 items or more
Maximum 5 impression level for Tinybubbles
Use Tinybubbles skill 5 times or more
Purchase maximum level 5 medal
Spend 3000 gold or more
Collect 10 stars or more
Purchase medal level 3 or above