I'm not entirely sure without reading it, but they might be related to the main characters from 'Rainbow Days'. It could be friends, family members, or even characters who had minor roles in the original but get more spotlight in the side story.
It could be about various things. Maybe it's about the side adventures or experiences of the characters from 'Rainbow Days'. It might focus on their relationships in more depth, or explore some events that are not covered in the main story.
It's mainly about the daily lives and relationships of a group of teenage boys. The story focuses on their friendships, emotions, and experiences growing up.
Well, it could be a story that involves the concept of creating or growing a rainbow in an online setting. Maybe it's about a character who uses digital means to make a rainbow appear, for example, by using special coding or in a virtual garden. It could also be a story that uses the idea of a rainbow as a symbol for something positive like hope or diversity in the online world.