Dumbledore could be a possible companion in some fanfictions. His vast knowledge and experience of the magical world would be invaluable. He could guide Harry and introduce him to different magical societies. Also, Hagrid might join in. His love for magical creatures would make him excited to see new ones in different parts of the world, and he could help Harry communicate with them.
Maybe Neville. He has grown a lot in his magical abilities and his courage. He could bring his knowledge of herbology, which might be useful in different parts of the world. Luna Lovegood could also be a great companion. Her unique perspective on magic would help Harry see things in a different light during his travels.
Hermione would be a likely companion. She loves learning and exploring, so she'd be eager to go on a traveling adventure with Harry. Ron might also tag along, especially if there's a chance of food and adventure. Neville could be another option. He has grown a lot in courage and his knowledge of plants could come in handy in different magical environments. Luna Lovegood would be a very interesting companion too. Her unique perspective on magic and the world would add a lot of fun and mystery to the journey.
In such fanfictions, one interesting scenario could be Harry Potter visiting the Great Wall of China. He might use his magic to explore the hidden parts of the wall that are not accessible to Muggles. Another could be his visit to the Amazon rainforest, where he discovers magical creatures unique to that area and has to use his skills to protect them from dark wizards who want to exploit their magic.
He could meet his future children, if he has any. They would likely be powerful wizards or witches with their own adventures. Also, he might run into the future versions of Hermione and Ron. They would probably be in important positions in the wizarding world, like Hermione might be a headmistress at Hogwarts or something.
He might meet versions of himself from different timelines or parallel universes. Also, there could be new and unique magical beings that the author creates just for the fanfiction. For example, a race of half - human, half - phoenix creatures.
The Weasley twins could be part of it too. Suppose Harry yells in excitement or anger about a new prank idea that the twins have come up with that might be a bit too dangerous. They could either encourage his yelling or try to tone it down, depending on their mood. And Malfoy might overhear Harry's yell and use it as an opportunity to taunt him, adding more conflict to the fanfiction.
In this 'harry potter goes to the sixth world fanfiction', we would expect Harry Potter. Besides him, there might be new wizards or witches native to the sixth world. They could have their own unique powers and personalities. Maybe there are also some half - magical beings that Harry has never encountered before. These new characters would add more complexity and freshness to the story.
Most likely, Harry Potter himself would be one of the main characters. He has a natural inclination for adventure and would be eager to explore the world on the train. Hermione Granger would also be there, with her vast knowledge of magic to help them out in different situations. Ron Weasley too, for his loyalty and friendship.
Hermione would definitely be one of his allies. She is smart and would be able to help him research about his new identity and how to control his powers. For example, she could find ancient texts in the Hogwarts library that relate to both the wizarding world and the Greek gods.
His friends from Hogwarts could still be his allies. Hermione would use her intelligence to help him understand his new situation. Ron would be there for moral support. Additionally, any friends or allies that Rias has in her world could also become Harry's allies. They might be magical creatures or other powerful mages.
Hermione would definitely be an ally. She's smart and would be able to help Harry research about his 'son of Mars' heritage, finding ancient spells or texts that could explain it further.