In the Land of Leadale, Vol. 4 (light novel)

Still Waters Run DeepCayna's life following her recent move to the countryside with her adopted daughter, Luka, is both peaceful yet eventful. One day, Cayna takes a trip to Felskeilo with Luka, Roxine the maid, and Lytt, the local innkeeper's daughter, in tow to check out the royal capital's River Festival. When they arrive, however, Cayna receivesword from a nearby Guardian that another Guardian Tower is running out of MP and needs Cayna's help. There's just one catch-the tower takes the form of a gargantuan whale! To make matters worse, the festival Cayna and her crew came to enjoy may be in danger... because the whale in question is swimming in that very river!