Well, it could be about Ash's journey with the Riolu egg. Maybe he has to protect it from various dangers in the wild. He might face off against Team Rocket who are trying to steal the valuable egg. Ash could also learn a lot about Riolu's species while waiting for the egg to hatch, like their natural habitats and behaviors.
One possible adventure is that Ash has to travel through a dangerous forest with the Riolu egg. There could be wild Pokémon that are attracted to the egg's energy and try to attack. Ash would have to use his other Pokémon to fend them off. Another adventure could be in a big city where there are thieves who target rare Pokémon eggs. Ash has to outsmart them to keep the Riolu egg safe.
One possible plot could be that Riolu is being chased by some bad guys who want to use its power. Ash rescues Riolu and they team up. As they journey, Riolu learns from Ash's kindness and determination. They enter Pokémon battles together, and Riolu's unique fighting style combined with Ash's strategies help them win. Also, their relationship could grow deeper, with Riolu becoming one of Ash's closest Pokémon companions.
You can try looking on fanfiction websites like FanFiction.net or Archive of Our Own. Just search for 'Ash gets a Riolu' in their search bars, and you might find some relevant stories.
Maybe it's a legendary Pokemon in disguise. In some fanfictions, legendary Pokemon often play important roles. It could give Ash the egg as a test or because it senses that Ash has a pure heart. Another possibility is that it could be a young trainer who can't take care of the egg anymore and trusts Ash to do a good job.
His friends like Pikachu for sure. Pikachu would be there by Ash's side, probably as curious as Ash about the Dratini egg. Brock might also be involved. He could use his knowledge of Pokémon to give Ash some tips on taking care of the egg.
Well, in the fanfiction, Ash might start by being super excited about getting the Dratini egg. He could be very protective of it, constantly checking on it and making sure it's in a safe place. Maybe he'd research all about how to take care of a Dratini egg, like the ideal temperature and humidity.
In this fanfiction, Ash might take really good care of the Pokemon egg. He would probably keep it warm and safe, waiting eagerly for it to hatch. Maybe he'd even talk to the egg, like he does with his other Pokemon friends.
One idea could be that Ash has a strange encounter in a mysterious forest. There, he finds a Riolu in distress. As he tries to help the Riolu, a strange energy transfer occurs, and he starts to take on some of Riolu's characteristics. He might gain Riolu's heightened senses, like its ability to sense auras more acutely. This could lead to new adventures as he has to adapt to these changes while still trying to pursue his Pokémon journey goals.
Adventure is also prevalent. Ash and Riolu go on various quests together, exploring new lands, encountering new Pokémon and trainers. These adventures not only test their skills but also strengthen their relationship as they face difficulties side by side.