One common theme is the exploration of different realities. Since Night Vale has such a unique and strange reality, when it crosses over with other universes, the differences and similarities in how they perceive reality are often explored.
One idea could be to cross it with a vampire hunter story. Have the characters from House of Night face off against a group of vampire hunters who don't understand their different kind of vampirism. It would create a lot of action and drama.
It's really hard to say who would be the most powerful. On one hand, in Fate Stay Night, Servants like Gilgamesh have incredible power. His Gate of Babylon contains countless noble phantasms. But in the Naruto world, characters like Naruto in his Six Paths Sage Mode are also extremely powerful. He has the power of the tailed beasts and can use all kinds of powerful jutsu. However, if we consider a crossover, it might be someone who can combine the powers from both worlds. For example, if a mage from Fate could learn to use chakra and combine it with their magic, they could be very powerful. Or if Naruto could somehow gain the abilities of a Servant, like the ability to use noble phantasms, he would be unstoppable.
In these crossovers, the theme of growth is quite common. Shirou starts as his normal self but through his experiences in the new world, he grows as a character. For example, in a crossover with the 'Naruto' world, he may learn new combat techniques and also gain more understanding of different kinds of power. Another theme is the exploration of new power dynamics. How his power compares to the powers in the new world, like if he's in the 'Bleach' universe, how his abilities stack up against Soul Reapers. And the theme of moral dilemmas also exists. He may face situations where the moral code of the new world challenges his own.
There's also a 'Night Vale and Welcome to Night Vale' crossover fanfic. It delves deep into the shared universe aspects, exploring how different aspects of the two shows can co - exist and influence each other. It has some really creative plot twists that keep you hooked.
Aphrodite from House of Night is also a great character. She's complex and often causes trouble. In a crossover, she could bring her mischievous side to a different setting. Let's say it's a crossover with a fairytale world. Aphrodite might be the one to manipulate the fairytale characters for her own gain, adding an interesting layer of conflict.
One unique feature is the combination of different universes. For example, when Saber is crossed over with a modern - day setting, it creates a contrast between her medieval values and the contemporary world. This leads to interesting character development as she has to adapt.
The 'under night visual novel' is a great piece of work. It offers a deep - diving experience into its fictional world. In this visual novel, you will encounter different characters, each with their own motives, personalities, and backstories. The story is not only about the main plot but also about the relationships between these characters. There are dialogues that are well - written, which can make you feel the emotions of the characters. The art style in the visual novel is also a big plus, as it helps to bring the story and characters to life vividly.
The most interesting part is the combination of different powers. In RWBY, we have the unique Semblances and in Fate Stay Night, there are powerful Servant abilities. When these are combined in a crossover fanfiction, it creates really exciting battle scenarios.
A crossover with the Persona series is also quite popular. The themes of the inner self and combat against otherworldly entities in both series can be blended together. The characters from Fate Stay Night could potentially enter the Metaverse from Persona and interact with the Persona users. This could lead to some really cool battles and character development.