She is Taichi Tanaka's older sister.
Haruka Tanaka is created by Evergreen and illustrated by Tomiyaki Kagisora as a minor character. She first appears in Tari Tari volume ? and Tari Tari episode 3: Swinging and Meeting.
She is first seen drinking in her room while wearing only her undergarments. Atsuhiro enters the room only to hop away in embarrassment. Haruka comes by and informs Atsuhiro that Taichi does not usually brings friends to his home.