Not having read 'The Darkness' makes it a guess, but many Icelandic novels explore themes like the power of the Icelandic landscape. It could be that in 'The Darkness', the harsh and unforgiving Icelandic environment plays a big role, perhaps representing the internal struggles of the characters. Also, themes of identity, both personal and cultural, are often explored in Icelandic literature, so that might be in there too.
Since I'm not familiar with 'The Darkness' Icelandic novel, we can make some assumptions based on Icelandic literature in general. One theme could be the passage of time and how it affects people and the land. Iceland has a long and complex history, and novels often reflect on how the past still lingers. Another possible theme is the supernatural. Icelandic folklore is rich with tales of elves, trolls, and otherworldly beings, and it wouldn't be surprising if 'The Darkness' incorporated some of these elements into its narrative, perhaps as a way to explore deeper psychological or spiritual aspects of the characters.
One of the main themes is the corrupting nature of power. In the novel, the political system twists and distorts the characters' values. Another theme is the loss of individual freedom. The main character is trapped in a system that controls every aspect of his life. Also, the idea of betrayal is prominent, as characters turn on each other in the name of political ideology.
One of the main themes could be the struggle against the unknown in the darkness. It might also touch on themes of survival and the human spirit's resilience.
The themes include the exploration of good and evil. The setting in the Congo makes the characters face their own morality. Racism is also a theme. The Europeans in the novel often look down on the African natives, which reflects the prevalent racist attitudes of that time. And there is the theme of isolation. Marlow is isolated during his journey, both physically in the African wilderness and psychologically from the people around him, which makes him question his own values.
One of the main themes is adventure. The characters are constantly on quests and facing various challenges in a fantasy world. Another theme is friendship. Despite their differences, the characters like Kazuma, Aqua, Megumin and Darkness form a unique bond as they journey together.
Probably one of the main themes is the struggle between good and evil. As the title implies, the characters might be falling into darkness, which means they are likely being tempted by evil forces or their own dark desires.
One of the main themes is imperialism. The novel shows the dark side of European imperialism in Africa, how it exploited the land and the people. Another theme is the loss of innocence. As the protagonist travels deeper into the Congo, he witnesses so much horror that his own sense of self and innocence is shattered.
Another theme is the coexistence of hope and despair. In many such novels, even in the darkest of times, there are glimmers of hope. Take 'The Hunger Games' for instance. The Capitol represents the darkness with its oppression, but Katniss's defiance and the hope of a better future for the districts are the light. This theme often makes the story more complex and engaging.
The theme of social class differences could also be significant. There may be barriers or tensions between characters from different social strata. This could influence their relationships, decisions, and the overall direction of the story.
The most obvious theme is the struggle between good and evil, where light often symbolizes good and darkness represents evil. For example, heroes in the story might fight against dark forces.