@justanothermanganerd
Usually I would agree but here no. There's barely anything adult about her. Author is just pushing the legal loli persona. She acts like a child, her room is like a child's and so on. At least Yuuto is kinda acting like a man. I'm not saying this ship should get down to business right away but if it's in the future whatever right ?
Though I have to admit that onee x shota is more enjoyable to me than oji x loli. Nevertheless, I'm sorry but this is basically the same thing as the main couple. That "she's an adult" is not fooling anybody.
Red Rice is a traditional dish normally eaten during celebrations eg. birthdays, weddings, some holidays, engagements, etc. There's even a phrase "let's eat red rice" that is the equivalent to "lets celebrate" in English. So that's what red rice means for those who ask.