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