Ato de Shimai Masu.

Ato de Shimai Masu. summary:

There's a secret about Rumika the Elementary Schoolgirl's older sister. That is, this sister who she loves so much is actually a lazybones around the house and is interesting in cosplaying. While cooking, cleaning, and helping with chores around the house, in order to be like this hardworking and wonderful sister, Rumika gives it her all. This is the long-awaited first chapter of the everyday life between these two casual, lovey-dovey sisters.