Lonely Castle in the Mirror 
by Mizuki Tsujimura 
translated by Philip Gabriel

QUICK SUMMARY
In a neighbourhood of Tokyo, seven students have been avoiding going to school for one reason or another. Unable to face their family and friends, they one day find mirrors in each of their bedrooms are shimmering. 

As they touch the mirrors, they're pulled into another world away from their lonely lives to a beautiful castle. Where they're met with a young girl explaining that there is a hidden key, and with that key the winner will receive whatever they wish.

FINAL THOUGHTS
Another winner from @curiously.katt. This one did hit close to home as someone who did not have a great school life. This book hits mental health and the struggles young people face. There's not a single person I didn't love about this book.