The main themes could include the exploration of the unknown. Given the title, it's obvious that the characters are delving into something not commonly known. Another theme might be transformation. As they experience the other side of the secret, they may change in some way. And loyalty could be a theme as well. Characters might need to be loyal to each other in order to survive or understand the secret world.
Secrecy is a major theme. The girl in the story usually has something she needs to hide, like her identity or her special abilities.
One similar light novel could be 'A Certain Magical Index'. It has a complex world - building with various factions and powers, much like 'the other side of secret light novel' might have. Another one is 'Overlord', which also delves into a hidden and often misunderstood world of the protagonist. And 'Re:Zero − Starting Life in Another World' is also a great choice as it has secrets and different sides to its story as well.
Fantasy is likely a main theme too. Since there's a secret door, it might lead to magical or extraordinary places. The other stories probably also have elements of the fantastical, like strange creatures or unusual powers, which all contribute to a fantasy - themed collection of stories.
One main theme could be the exploration of the self. In 'The Secret Sharer', the protagonist's encounter with his double makes him question his own identity and moral boundaries. Another theme might be isolation. The characters often seem to be alone in their experiences, whether on a ship at sea or in other settings.
Well, I think family could be a theme. In many short story collections, there are often tales that revolve around family relationships. Also, nature could be a theme considering the mention of a pool which is a part of nature. The stories might explore how characters interact with nature.
Common themes might include the exploration of a particular historical period, such as the social structure. For example, it could show how different classes of people interacted during that time.
I don't know as I haven't read it. But it could be the hero who defeated the last boss, and maybe some companions who joined the journey to the other side.
Well, different 'Secret Side Story' might have different main events. For example, if it's a fantasy 'Secret Side Story', there could be events like a hero's secret quest to find a magical item. Maybe there are hidden romances or unforeseen alliances that are revealed only in this side story. It all depends on the genre and the overall plot it belongs to.
One main theme is the mystery of the other side. Since it's not fully explored in the show, fanfictions often try to uncover its secrets. Another theme is the connection between the living and the dead. Characters from the other side can interact with the living in various ways, which is often a big part of these stories.
Well, it could be about facing one's fears. The 'other side of darkness' might represent all the things we are afraid of, and the novel could be about characters' journeys to confront those fears. For example, it could show how they grow and change as they face the things that are in the dark, both literally and metaphorically.