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