Well, a cool concept is the reconstruction of the world. In 'undertale after genocide fan fiction', the world that has been devastated by the player's actions might be shown in the process of trying to rebuild. It could involve new forms of leadership among the remaining monsters, new rules and social structures emerging. Also, the psychological state of Flowey could be further explored. He's already a complex character, and in the aftermath of genocide, his nihilistic view might change or intensify in interesting ways.
Some fan fictions in this area might explore the idea of time - related concepts. Maybe there are attempts to reverse the genocide through time - travel or some form of magic. This could bring up all sorts of paradoxes and moral dilemmas. There could also be the concept of a second chance for the protagonist, where they try to make amends for their previous actions. This might involve them facing the ghosts of the monsters they killed, both literally and metaphorically, and trying to earn their forgiveness.
One concept could be exploring the psychological state of the character who undertakes the genocide route in more depth. For example, how they gradually lose their sense of morality and what drives them to keep going despite the horror they are causing.
The protagonist who carried out the genocide is often a central focus. Their journey of coming to terms with what they've done is a major part of the story. Also, Sans is frequently in the spotlight. Given his awareness and his final stand in the original genocide route, fan fictions might explore his continued existence or his possible return in the post - genocide world.
One interesting concept could be an OC that is a powerful mage in the Undertale fanfic world. They could have unique spells that interact with the game's existing magic system in unexpected ways.
Another aspect could be the expansion of the lore. In undertale overgrowth fan fiction, the lore might be developed further by combining the backstories of both universes. This could involve things like how the magic systems interact or what new threats emerge from the combination. It can also explore different endings based on these new lore developments.
One interesting concept could be the combination of magic from Harry Potter and the unique battle system of Undertale. For example, a character might use a Patronus charm in the style of an Undertale monster's attack. Another concept could be the interaction between Hogwarts houses and the different areas in Undertale. Like Slytherin characters might be more drawn to the more dangerous or morally ambiguous parts of the Undertale world.
One interesting concept could be the crossover of characters' personalities. For example, how the determination trait from Undertale might interact with the more mysterious elements in Deltarune. Another could be the exploration of different timelines. Since both games have some elements related to time and alternate realities, a fanfic might delve into how these timelines could cross or affect each other. Also, the unique magic systems of both could be combined in creative ways, like how the soul powers in Undertale might work with the magic in Deltarune.
One interesting concept could be the combination of Naruto's ninja abilities with Undertale's unique battle system. For example, Naruto's shadow clones might interact in a strange way with the bullet - hell - like attacks in Undertale. Another concept could be the characters from both universes meeting and forming unexpected relationships. Naruto's friends could meet Sans or Papyrus from Undertale and have to learn to communicate across their very different cultures.
One interesting concept could be alternative endings. Fanfiction often explores what would happen if different choices were made during the main story. For example, a fanfic might explore a scenario where the protagonist befriends all the monsters in a completely different way than in the original game.
In undertale chara crossover fanfiction, a cool concept is the power dynamics. Say Chara crosses over into a world with super - powered beings. Chara's determination - based abilities could be pitted against new and strange powers. This can create intense battle scenes and strategic confrontations as Chara tries to figure out how to deal with these new threats or allies.
One interesting concept could be alternate storylines for the characters. For example, exploring what would happen if Bell Cranel had a different Familia. It could lead to completely new adventures and character developments.