Here is the full list of all 26 Magical Diary: Horse Hall achievements. It takes around 15-20 hours to unlock all of the achievements on Windows.
You maxed out your Merits.
You can't go home again.
You helped Ellen form a school conspiracy
You became a full member of the Rose And Wasp.
You received five detentions in one game.
You broke your oath and lost your magic - for now.
You maxed out your Cute.
You maxed out your strength.
You had an escort for the May Day Ball.
You maxed out your Weird.
You maxed out your smarts.
You maxed out your Green Magic.
Too many demerits ended your school year.
After a year locked in the school dungeons. Nasty.
You maxed out your Black Magic.
You maxed out your White Magic.
You refused to attend any classes!
You retrieved the elusive stuffed bunny.
You maxed out your Red Magic.
Someone has locked lips with you.
You made it through the school year!
You maxed out your Blue Magic.
You maxed out your Stress.
Oops! Accidentally married.
You won the election for class treasurer.
You received detention