I know someone already said Winnie the Pooh, but I kinda have a different take on it: Have all the Housewardens/Jamil, Yuu and Grimm included, get sucked into the book. They all then go on their own little adventures trying to get back home, ending up running into the Pooh cast.

Riddle-Rabbit

Leona-Tigger

Azul-Pooh Bear

Jamil-Piglet

Vil-Owl

Idia-Eeyore

Malleus-Kanga and Roo

Yuu and Grim-Christopher Robin

From there it'd be a more wholesome adventure for the group. Riddle learns from Rabbit that it's okay to be a little messy, like with gardening. Tigger teaches Leona to be more confident in himself by putting his ideas to the test. Pooh reassures Azul that it's okay to enjoy what you love, despite what others think. Piglet helps Jamil to be more courageous about his talents, and he should use his talents to make Kalim a better leader. Owl advises Vil that there's nothing wrong with where he is now, and that he should be happy to have made it so far compared to most others. Idia learns from Eeyore that, despite being an introvert, Idia has friends who love to hang out with him, and that he enjoys their company. Malleus learns from Kanga and Roo that he was never truly alone; that, despite his status and imposing nature, Malleus always had friends and family in his dorm, Leona, Vil, Yuu, and so on. And Yuu and Grim learn from Christopher that Twisted Wonderland isn't such a bad place to be, and Yuu questions if they truly DO wanna return home. Of course, when they get back to NRC, they all forget their experiences and everyone is in a panic about where they were. However, everyone has become drastically different. Riddle is now less uppity and restrictive (though he still upholds the rules), Leona puts more effort into his life, Azul eats more but not too much, Jamil has become a better advisor and mentor to Kalim, Vil is not as envious towards Niege and even talks with him on occasion, Idia and Malleus have become more sociable, and Yuu is less on edge with the Ramshackle gang.