@Power4ullk1w1 I honestly like the idea of the piano, however, placing Nano in the white room wouldn't fit the story as well. This is because Rentaro's appearance was only temporary. It's true that I'll include characters from other anime, but not all of them will stay.
First, there are the characters who will remain in the story. An example would be Ai, who remains Honami's best friend. These characters will accompany Kiyotaka and Honami throughout the story and will have their own moments.
Second, there are the temporary characters. These only appear for comedic moments. An example would be Rentaro. He appeared mainly to humorously explain Honami's love for Kiyotaka. It's possible that Rentaro will appear again in the story, but not be involved in the plot.
Third, the long-term characters. These characters are mentioned in the story, but there's still a long way to go before they appear. Johan and Tenma, for example, were mentioned earlier, but there's still a long way to go before they make an appearance.
I hope this helps you understand how I'm writing the story.
A small spoiler I'll give you about the story is that the characters from Sakamoto Days and Spy Family will become involved later on. :D
