In The Land Of Leadale Vol. 4 (Light Novel)

In Vol. 4, Cayna is enjoying a peaceful life in the game world of Leadale together with her step-daughter Luka and the villagers. One day, she sets off once again for Felskeilo together with the innkeeper’s daughter Rit and maid Roxine to take Luka to meet her eldest daughter, Mai Mai. Though attacked by bandits along the way, they make it safely to Felskeilo, and there, Cayna receives a message from a guardian asking her to save the Guardian Tower, which is running critically low on MP. To her surprise, Cayna finds that the tower is actually a gigantic blue whale that swims underwater and is over 100 meters long!
Notice: This book is written in Japanese.