The 'Don't tell anyone else's smile is so beautiful...ಥ‿ಥ
By the way, Sora.. doesn't seem like showing her sadness around people.
Behind her smiling face, she hides it.
Maybe something happened in her house that she moves to Kyushu but that woman is her mom?
She's talking about her mom?
Hmm.. can I assume that she has a bad relationship with mom...?
A common reason for people to instinctively hide away their feelings would be a background of abuse or neglect (which is a form of abuse of course) during their childhood. If a child learns that nobody will respond when they show signs of need or distress, or if these hints of weakness and vulnerability are punished or exploited, then they will quickly learn to bottle up these vulnerable emotions. They become things that they have to deal with themselves - things that need to be kept separate from the outside world.
Based on what we see about the relationship of Sora and her Mother so far, and the things she says when talking about her mother, it would be likely that she was victim of some sort of abusive upbringing - though we of course cannot yet tell the details here - and there is a good chance that this is also why she bottles up about these kinds of emotions.
