Well, 'Densha Otoko' isn't real. It's more like a made-up tale that captured people's imaginations. The characters and events were crafted for entertainment.
Their relationship in the fanfiction is likely to be full of mutual understanding. Since they are getting married, they must have a deep connection. Takato might be the more gentle and patient one, while Rika could be the strong - willed partner. They balance each other out.
Overall, the manga and anime of Dakaretai have similar storylines, but the anime might condense or expand on some events for better pacing. Also, character designs could vary slightly in the anime.
It's mainly about the adventures and challenges faced by the characters in a unique setting. The story is full of twists and turns that keep you engaged.
The 'densha otoko real story' is about a man's experiences on the train. It might involve his daily commute, the people he meets on the train, and the events that occur during his train rides.
A fanfiction might focus on the relationship between Takato and Rika evolving. At first, they might have their differences as we see in the original series. But in the fanfiction, they could start to understand each other better. For example, Takato could learn from Rika's more assertive nature, and Rika could appreciate Takato's kind heart. They could then become closer friends and better partners in Digimon battles.
Social media groups related to Digimon can also be a good source. For example, on Facebook or Reddit, there are groups where fans discuss all things Digimon, including fanfiction. You can post a request asking for Female Takato fanfictions, and chances are, someone will be able to point you in the right direction. Just be sure to follow the group rules when posting.
I'm not sure specifically about 'lemon' (suggestive/erotic) fanfiction as it goes against many platforms' rules. However, there are likely many great non - inappropriate Renamon and Takato fanfictions out there. You can try searching on general fanfiction websites like FanFiction.net or Archive of Our Own, and filter for the appropriate rating and genre.