I don't know who the author of 'tumbling through time novel' is. There are so many novels out there, and without more information, it's hard to determine the author.
I'm not sure specifically as I haven't read it. It could be about a character who is experiencing different time periods in a rather chaotic or uncontrolled way, like tumbling from one era to another.
One idea could be to write a fanfic where the characters in Tumbling Towers face a mysterious force that shakes the very foundation of their tower. Another could be a story about a character's journey to rebuild a fallen Tumbling Tower, full of challenges and new friendships.
Often, the lead builder characters are quite popular. They are usually the ones with the most skills and knowledge about constructing the towers. Their determination and leadership make them interesting to write about.
One idea could be to create a story where the characters from Tumbling Towers face a new and unexpected challenge in the tower, like a strange magical force that makes the blocks move on their own. Another idea is to write about the backstories of the players, how they got involved in the Tumbling Towers game in the first place. Maybe there's a character who has a secret ability that helps them in the game, and the fanfiction could explore how they discovered and developed that ability.
In general, the Evangelion mangas are considered good. They expand on the anime's universe, providing more depth and character development. However, it depends on personal preferences as some might find the style or pacing not to their liking.