One popular storyline could be Naruto and Tiki teaming up to face a new and powerful enemy. Maybe a villain from another dimension who threatens both their worlds. They would have to combine Naruto's ninja skills with Tiki's unique abilities to defeat the foe.
Naruto's chakra - based powers, such as his Rasengan, could be combined with Tiki's more magical powers. For example, Naruto could use his chakra to enhance Tiki's spells, making them more powerful.
In many Fire Emblem Grima x Tiki fanfictions, the theme of trust is key. Since Grima is a character that is often not trusted, the development of trust between him and Tiki can be a major plot point. Another common theme is the idea of prophecy. Given the rich lore of Fire Emblem, prophecies related to both Grima and Tiki can be explored in fanfiction, such as how they might fulfill or defy certain prophecies through their relationship.
You can start by looking on fanfiction websites like Archive of Our Own (AO3). There are often tags related to 'Fire Emblem', 'Grima', and 'Tiki' which can help you narrow down the search. Another option is FanFiction.net, although the tagging system might be a bit less precise. You could also check out some Fire Emblem - related forums where fans might share their favorite fanfictions about these two characters.
One possible plot could be that Allen is a curious character who was exploring an old haunted house. His tiki ghost hand, which has a mind of its own, reaches out to touch an ancient door. As it tries to pass through the door, it gets stuck. Allen then has to figure out a way to free it, perhaps by using some magic spells he learned from a local witch.
A common theme is the exploration of their different personalities. Robin is often depicted as intelligent and strategic, while Tiki has her own charm and naivete. Their interactions based on these traits are frequently explored.
They are a popular pairing because they are both very unique characters. Robin is a tactician with great intelligence, and Tiki is a powerful dragon. Their different natures create an interesting dynamic.
Perhaps in the fanfiction, the Tiki hand getting stuck is a sign of some sort of magic at work. Maybe the door is enchanted, and the only way to free the hand is to solve a riddle or perform a specific task. This could lead to an adventure for Allen as he tries to figure out how to free his hand.
The 'Kon Tiki' novel is mainly about Thor Heyerdahl's epic adventure on the Kon - Tiki raft. It tells of his journey across the Pacific Ocean to prove that ancient South Americans could have reached Polynesia by raft.