There could be a theme of mystery as well. The 'estrus' part of the estrus gymnasium gives an air of the unknown. What is special about this gymnasium? What secrets does it hold? These questions could drive the plot and add an element of mystery to the light novel.
I'm not sure if there are specific well - known light novels directly related to 'estrus gymnasium'. It might be a very specific or even a made - up concept. However, there are many light novels in the general sports or school - life genres that could potentially have some tangential connections.
One possible theme could be self - reliance. The title 'leave this to me' implies that the main character takes on challenges by themselves, suggesting a theme of being able to depend on one's own abilities.
A theme of isolation might be explored as well. If the dead are rising, society could break down, leaving individuals or small groups isolated. This could lead to a sense of loneliness and the need to find new connections in a world full of danger. Additionally, there could be a theme of the unknown. The nature of the rising dead, why it's happening, all these are mysteries that could drive the story.
One possible theme could be adventure. If 'fenglingtianxia' implies a vast world or realm, the characters might embark on an adventure through this world, like exploring new lands or seeking treasures. And if 'wangfei' is involved, there could be a theme of royalty or court intrigue. The wangfei might be involved in political struggles within the court.
One possible theme could be friendship. Geniuses coming together often form strong bonds and support each other through various challenges.
One possible theme could be loneliness. Since it's about a deserted woman, she is likely to be alone and deal with the emotions that come with isolation. Another theme might be self - discovery. As she is in a difficult situation, she may start to find out more about herself and what she really wants.
Power and leadership could be a theme. Since it's about a 'cosmos ruler', it might explore how one gains, wields, and is affected by power in a vast universe.
Another theme might be self - discovery. The main character could go through a journey of understanding themselves better throughout the story, and the ending could be a culmination of this self - discovery. They might realize their true desires, values, or even their own strengths and weaknesses.
Since I haven't read it, it could be about friendship. Many light novels explore the deep bonds between characters, so it might be a theme in 'Five Days Light Novel'.
If we consider light novels in general, themes like friendship, love, and power struggle are common. So in 'immortal invisible light novel', there could be a theme of friendship between an immortal and a mortal, or a power struggle between those who are invisible and those who are not. Love could also play a part, perhaps a love story between characters where one has the immortality or invisibility factor and how that affects their relationship.