One common theme is Saiki's struggle with his powers. In many fanfics, he tries to hide his psychic abilities from others while still having to use them at times, which leads to comical and tense situations.
One common theme is the reader having some sort of special relationship with Saiki. It could be a friendship or a romantic relationship. For example, the reader might be the only one who truly understands Saiki's powers and they form a deep bond.
One common theme is the exploration of their unspoken feelings. Since in the original anime there's a lot of unexpressed emotions between them, fanfics often delve into how they might come to terms with their feelings for each other.
Sure. 'The Ordinary Life of a Psychic' is a great saiki k fanfic. It delves into Saiki's daily experiences in a really interesting way, showing his attempts to blend in while dealing with his extraordinary powers.
One common theme is the reader character having special powers or abilities that interact with Saiki's powers in interesting ways. For example, they might be able to nullify his telepathy accidentally.
One challenge is staying true to Saiki's character. He's very stoic and doesn't like to get involved in unnecessary things. So when writing with a female character, it's hard to make their interactions seem natural without forcing Saiki to be too out of character. Another challenge is creating a unique female character. There are so many existing characters in the Saiki K universe that it can be difficult to come up with a new one that stands out.