Well, a lot of 'dark tenth doctor fanfiction' plays with the idea of the Doctor losing his moral compass. For example, in some stories, he's forced to make really tough choices that make him question his very essence. These stories often explore the grey areas of his character and are quite thought - provoking. They can be really interesting to read as they break away from the more traditional, heroic view of the Doctor.
You can start by looking on fanfiction websites like Archive of Our Own. There are a lot of different categories and tags, so you can search specifically for 'dark tenth doctor fanfiction' and find a bunch of stories.
One of the best is 'Blink'. It has a really unique and creepy concept. The Weeping Angels are introduced, and their ability to move when not being watched is both terrifying and fascinating. The Doctor has a more minor role in this story, which actually adds to the mystery and shows the far - reaching impact of his actions even when he's not directly present.
In these fanfictions, a frequent theme is time - related chaos. Since they are both time - traveling Doctors, they might accidentally disrupt the time - space continuum and have to fix it together. There's also the theme of self - discovery. As they interact, they might learn new things about themselves. For instance, the Tenth Doctor could learn to be more carefree from the Eleventh Doctor, and the Eleventh Doctor could learn about the importance of taking things seriously from the Tenth Doctor. Additionally, the theme of nostalgia can be present. The Tenth Doctor might remember his past adventures, and the Eleventh Doctor could be intrigued by them.
Another interesting one is 'Parallel Worlds'. In this fanfiction, it explores different parallel universes where the Tenth Doctor and Rose's relationship takes on various forms. It's full of creative ideas and really makes you think about the possibilities of their relationship.
One popular one could be 'A New Beginning' where they start their married life on a new planet, facing all kinds of adventures together. It's full of their typical banter and sweet moments.
One popular 'dark doctor fanfiction' could be about a doctor with a hidden, malevolent agenda in a post - apocalyptic world. He might use his medical knowledge not to heal but to control the remaining survivors. Another could involve a doctor in a haunted hospital, where his dark past is intertwined with the spooky happenings in the building. And there might be stories where a doctor is part of a secret, unethical experiment, creating a very dark and suspenseful plot.
One popular theme is the adventure aspect. Fans often write about the baby growing up in a world full of time - traveling and alien encounters, just like the Doctor and Rose had. Another theme is family. It could be about how the Doctor, Rose, and their baby form a unique family unit, dealing with the challenges of being part of different species. Also, the theme of protecting the baby from various threats, both from within their own universe and from other dimensions, is quite common in these fanfictions.
In a 'Tenth Doctor meets Eleventh Doctor fanfiction', they might start by being a bit competitive. The Tenth Doctor could show off his sonic screwdriver skills, while the Eleventh Doctor would counter with his own unique way of using it. Maybe they'd end up teaming up to face a common enemy, like a powerful Dalek or a new kind of alien threat. They could also have some interesting conversations about their different experiences with their companions.
Adventure is another theme. Since they travel through time and space together, many fanfics have them going on all sorts of exciting adventures, whether it's saving a planet or exploring a new era. It adds to the overall charm of their relationship as they face these challenges together.
Some popular Tenth Doctor novels include 'The Stone Rose'. It's a great adventure that really captures the essence of the Tenth Doctor's charm and his knack for getting into tricky situations.