Yuki Yuna Is A Hero: A Sparkling Flower (Hanayui no Kirameki, also translatable into Brilliant Bouquet) is a 2017 mobile Tower Defense game based off of Yuki Yuna is a Hero. The game is a crossover between the various works in the franchise.
One day during club activities, the Hero Club is mysteriously transported back into the Jukai. They all have their Transformation Apps back despite the fact that they aren't Heroes anymore. After fighting with Vertex, a girl named Hinata Uesato appears. Hinata says that they're in a world inside of the Shinju. The Shinju has summoned Heroes from all eras to help battle rebellious gods that could lead to chaos.