Survival is a common theme. Since Riddick is often in harsh environments in his own story, when crossed over into other universes, he still has to fight to stay alive. For example, if crossed with 'The Hunger Games' universe, he'd have to use his skills to outwit the other tributes and survive the deadly games.
One possible plot could be that Riddick somehow gets transported to the Naruto universe. He could initially be seen as a threat, but then he teams up with Naruto and the others to fight a common enemy, like a new powerful Akatsuki member who has powers similar to some of the creatures in Riddick's world. Riddick's combat skills and his ability to see in the dark could give the Naruto gang an edge in battles.
One great 'riddick crossover fanfiction' could be where Riddick crosses over with the 'Alien' universe. In such a story, Riddick's survival skills would be put to the ultimate test against the deadly xenomorphs. His ability to see in the dark would give him an edge, but the aliens' strength and stealth would still pose a huge threat.
Well, it could start with a common enemy. There could be an entity that is a threat to both Inuyasha's world and Riddick's. This would force them to team up. For example, a powerful demon in Inuyasha's world has some sort of connection to a dangerous alien race in Riddick's universe. They would have to combine their combat skills, with Inuyasha's swordsmanship and Riddick's hand - to - hand combat abilities.
Inuyasha is impulsive and hot - headed. Riddick is more of a lone wolf, brooding and calculating. Their initial meetings would probably be full of tension. Inuyasha might see Riddick as a threat to his territory or his friends. Riddick would likely be suspicious of Inuyasha's demon side.
I think Kakashi and Riddick would make an interesting pair. Kakashi is a highly skilled ninja with a lot of wisdom, and Riddick has his own set of skills and street - smart knowledge. They could exchange ideas about combat strategies. Also, Hinata and Riddick could be an unexpected but interesting pairing. Hinata's gentle and shy nature could be a foil to Riddick's rough exterior, and she might be able to show him a different way of looking at things in the Naruto world.
Another plot could involve Harry Potter and his friends being stranded in a world similar to where Riddick comes from. There, they must rely on Riddick's knowledge of the harsh environment and his unique fighting style to survive. Riddick could also learn about magic from them, leading to some interesting interactions.
Obviously, Harry Potter and Riddick would interact. Harry, being the main hero in his world, would be curious about Riddick's strange abilities and his rough - and - tumble way of life. Riddick, on the other hand, would likely be suspicious of Harry at first but then come to respect his magical powers.
Since 'lemon' usually refers to something not suitable, we should focus on proper Riddick fanfiction. In general, good Riddick fanfiction often features his survival skills. He is a tough character, so the stories might show him in dangerous situations and how he overcomes them.
There are fanfictions that focus on Riddick's relationships. Some might explore a romantic relationship between him and a new female character, perhaps a strong warrior from a different planet. This relationship could add a new layer of complexity to his character as he has to balance his solitary nature with his feelings for someone else. Also, there could be stories about his friendship with Johns, showing how their relationship might have developed differently if certain events in the movies had changed.