Puriimo ~Please teach! My Sister~

Main character witnesses an angel coming down from the sky in a nearby park. Surprisingly, she turns out to be the new school teacher who needs teaching practice on Earth to become a full-fledged instructor in Heaven. If her angelic heritage is revealed, she is going to be disqualified, so she suggest to live together with protagonist and his sister. Teacher is a disaster at doing house chores, and sister wants to make memories with her brother before going to study in Vienna. Another summer story starts here.

[From vndbreview]