I'm calling it now, Touko is actually Satoru's mother. Her elder sister took the child in because she was likely in a better position (older, married, etc.) but doesn't really care for the boy. Touko gets the chance to get her life together, the boy gets a family, everyone wins. Now it's all gone wrong and she feels responsible which is why she's going so far for him despite acknowledging she's not really qualified for this at all. Does Satoru know it's his 'Aunt'? I don't think he cares, hikikomori is a sad life and he's just happily having someone pay attention to him at the moment.