I wish this series could have been 12 minutes instead.
There’s nothing much to learn here asides from Atsumi, who doesn’t grow despite taking in calcium and drinking milk. She also takes Atsushi with her whenever she goes to the grocery store. Again, Atsushi gets mistaken as an adult when he asked the guy in the bunny costume for some candy. But again, a very funny and heartwarming episode. Heartwarming in the sense that Atsumi took Atsushi’s hand before the credits roll.
BTW, Atsushi reminded me of that Robin Williams’s character in that movie, Jack, where he ages four times faster than normal children due to progeria. Except that, the aging caused him to look like a 40-year old man. In this anime, Atsushi probably looks like in his late twenties or early thirties. So, I don’t think he’s diagnosed with progeria or Werner syndrome because he looks attractive. If you look at how people who were diagnosed with this kind of genetic disorder looked like, they don’t look pretty.