One possible theme could be isolation. Kirby might be alone in a world filled with darkness, which emphasizes his struggle. Another theme could be redemption. If there are characters that have been corrupted, Kirby could try to redeem them.
The themes in a Kirby Dark Story could include survival. Given that it's a 'dark' story, Kirby would be constantly fighting for his life against stronger and more dangerous foes. Also, the theme of discovery could be present. As Kirby battles through this new, darker world, he discovers new things about his powers and the nature of the darkness around him. For example, he might find out that the darkness is linked to an ancient evil that he has to stop.
One possible theme could be friendship evolving into something more. Maybe Kirby and Scarfy start off as just friends, and the kiss represents a new level of their relationship.
Isolation could be a theme. In the dark, one can feel very alone. If it's a story about a person in a dark place, they might be cut off from others and have to deal with their situation by themselves. Also, survival can be a theme. If the 'in the dark' situation is dangerous, like in a dark cave full of hazards, the characters would be focused on surviving.
One possible theme could be fear. The very idea of a dark house often evokes a sense of unease and terror. Another theme might be mystery. There could be secrets hidden within the walls of the house that the characters are trying to uncover. For example, the mystery of what happened to the previous owners or what lurks in the attic.
One possible theme could be fear. The darkness of the room can symbolize the unknown, which often induces fear in people.
Isolation could be a theme. A dark tale might be set in a desolate place or the characters might be isolated in some way, which adds to the overall sense of gloom. Also, the theme of loss can be present. This could be the loss of a loved one, of innocence, or of hope, all of which contribute to the darkness of the story. For example, in a story where a character has lost their family in a tragic event, it sets a very dark mood.
Another theme might be isolation. At night, especially if it's very dark, a person can feel alone and cut off from the rest of the world. This sense of isolation can be a strong theme in the story.
The title 'la guerra sucia' gives some clues about possible themes. One theme could be the corruption that often accompanies war. This could be in the form of military or political corruption, where people in power use the chaos of war for their own gain. Another theme could be the destruction of innocence. War has a way of shattering the lives of the innocent, and this story might explore how ordinary people, especially children and the vulnerable, are affected. Also, themes of resistance and the fight for justice in the midst of a 'dirty' war situation could be part of the story.
Another theme might be friendship. Even in a dark future scenario, the characters could come together and use their friendship as a strength to overcome the challenges posed by Sombra. In many MLP stories, friendship is a central theme, and it could be incorporated into this fanfiction concept as well. For example, Kirby might form an unlikely friendship with the ponies and together they face Sombra. Also, themes of redemption could be present. Maybe Sombra has a chance to change his ways in this dark future storyline, adding an interesting layer to the plot.
Fear is a likely theme. The darkness of the room can symbolize the unknown which often induces fear in people.
One possible theme could be mystery. Since it's a 'dark gumball story', there are likely elements that are not immediately clear, like the origin or purpose of the gumball.