Opening theme - "Hiyoku no Hane" (比翼の羽根) by eufonius.
Taking place right after episode 2, the story takes a different route from previous episodes and focuses on Akira rather than Kazuha. Haruka learns about her past and that she and Kazuha are half-sisters who were born on the same day. He remembers playing with Akira as a child a long time ago, the day she lost her pendant; the only memento from her mother, and desides to help her find it. After digging around looking for the pendant, they go back to Akira's home to wash themselves.
Ending theme - "Pinky Jones" (ピンキージョーンズ) by Momoiro Clover (ももいろクローバー)
Points of Interest
Haruka remembers the time he and Akira spent together as children, much to Akira's joy.
Akira progresses much faster in her relationship with Haruka than her sister did, as she already had fond memories and feelings for Haruka.
At the end of the episode, Akira takes the records on her, in the hope of finding her mother.
Stitched screen captures from this episode (NSFW):
See the full gallery of screen caps from this series here.