Who are the best characters to include in a Hatsune Miku x Luka fanfiction besides them?

One idea could be a music competition where Miku and Luka are the top contenders. They start off as rivals but as they learn more about each other's music styles and the passion behind them, they become friends and collaborate on a new song. Another plot could involve them traveling through different musical dimensions together, exploring new sounds and rhythms, and using their unique voices to solve the mysteries of these strange musical worlds.

In some ichigo x hatsune miku fanfiction, there could also be secondary characters. For example, Ichigo's friends from his anime might make an appearance. They could be initially skeptical of Miku, being from a different kind of world. Or perhaps there could be some of Miku's digital friends or producers who get involved in the story, adding more layers to the plot as they try to understand Ichigo and his world.

Nendo could be a great addition. His simple - minded nature can add a lot of humor. For example, he could misunderstand the relationship between Saiki and Kaidou and try to get in on their 'adventures' in a really clumsy way.

Lapis Lazuli could be a great addition. She has a complex relationship with Peridot, and her presence could add some drama and depth. For example, she might be initially suspicious of Steven and Peridot's friendship, thinking that Steven is influencing Peridot too much. But over time, she could come to see the positive aspects of their bond.

Jimmy Olsen could also be a great character to include. He is Superman's friend and colleague at the Daily Planet. His loyalty and his ability to get into some sticky situations can add a touch of humor and also some interesting sub - plots to the Supergirl and Superman fanfiction.

Master Roshi could also be a great addition. His old - school ways and his comical reactions to Vegeta and Bulma's relationship can be really entertaining. For instance, he could give some really strange relationship advice to Vegeta based on his own limited understanding of modern relationships.

Metro Man could be a great addition. His presence could add some tension or an interesting dynamic, especially considering his past relationship with Megamind. Minion, Megamind's loyal sidekick, is also a must - include. He could provide comic relief and his unique perspective on Megamind and Roxanne's relationship. And maybe the Warden, who could be involved in some sort of prison - related subplot or just add to the overall chaos in the story.

Sasuke could be a great addition. He might initially be skeptical of Naruko's newfound bond with the Kyuubi, but then come to see the potential in it. Kakashi could also be included as he has a lot of knowledge and experience. He could offer guidance to Naruko on how to handle the Kyuubi's power. Another good character would be Jiraiya. He could have some interesting insights into the relationship between Naruko and the Kyuubi, having known about the Kyuubi for a long time.

The King and Queen of the kingdom. Their presence can bring in the political and parental aspects. They might have different views on how Rapunzel and Cassandra should handle certain situations, which could create more conflict and plot twists.

Their relationship can be developed through shared musical experiences. For instance, they could start by collaborating on a single song. As they work on the lyrics, melody, and production, they get to know each other better. Their different musical tastes can either clash at first and then gradually blend, or they can immediately find harmony in their differences.