That is Kyoko Otonash's apron from Maison Ikkoku. I am pretty sure Reisen was wearing a similar one earlier, but then again it is such an iconic apron that I might be thinking of another touhou series.
I didn't upload it because I didn't think it was quite up to Danbooru standards. But if that's the winner, then maybe it's worth having it for reference.
Jeez...such a mess!NO!Hey!You three, it's nap time already!Come on! Nappy time?H-Hey!!Today, like most days, the children have transformed into "selfish-sauruses"...*struggle**struggle**nom**nom**nom*Hello, everyone. Reisen here.*nom**fwaff**fwaff*