岡野 瀬奈

The oldest sister in the Okano family. She is 21 years old.

She is an office lady at a trading company. She is involved in developing a new business project at the company and brings home "prototypes" for her mother and Kana to try out.

She is happy to have a new family member who responds to her underwear. She enjoys embarrassing Ryouta by wandering around the house in her underwear and showing him how to changes her clothes.

She also makes Ryouta try out the prototypes she brings from work.

From official site.