One common theme is friendship. The OC often becomes a good friend to Jim, sharing in his office antics and providing support. For example, in many fics, they bond over their shared sense of humor.
Well, I'm not sure specifically about 'jim halpert x kelly fanfic' but in general, fanfics often take characters from a show and put them in unique situations. It could be that in these fanfics, they might be in a different work environment, or perhaps they meet under unexpected circumstances. You might have to dig a bit to find the really good ones, but they're likely out there.
A plotline could involve a love triangle. For example, Kelly is interested in Jim, but Jim is already in a relationship with someone else, and Kelly has to compete for his affections. Or perhaps Jim is initially oblivious to Kelly's feelings, and she has to find creative ways to make him notice her.
One great 'jim halpert oc fanfiction' is 'Jim's New Beginning'. It shows an original character coming into Jim's life at Dunder Mifflin in a really interesting way. The interactions between Jim and the OC are both humorous and heartwarming.
Maybe Jim is the protagonist who goes through various adventures and experiences. Or, he could be a key figure influencing the events in the story. Without more details, it's hard to say exactly.
Yes, Jim Gaffigan is considered a clean comic. His humor often focuses on relatable and family-friendly topics without excessive vulgarity or offensive content.