|Age||19 (volume 1)|
|Relatives||Kazuki Hoshino (Younger Brother)
Maria Otonashi (Sister-in-Law)
Luka Hoshino is the older sister of Kazuki Hoshino by three years.
Luka is usually wearing only her underwear around the house, much to Kazuki's annoyance.
Luka can be teasing towards her younger brother, Kazuki. She has a carefree attitude as she walks around the house with just an underwear despite her brother constantly insisting her not to. Once she even fell asleep while her brother was answering her question.
Luka first appeared when Kazuki was looking at a photo of Kasumi Mogi, teasing him about looking at lewd pictures on his phone. When she guessed that he was looking at a picture of Mogi, Kazuki was surprised. Luka revealed that she saw Mogi's name displayed on his phone when Mogi called him. Luka then inquired about her younger brother's relationship with 'Mogi-san'. While he was in the process of answering her, she had quickly dozed of to sleep much to Kazuki's amazement.
Luka and Kazuki share a room and also a bunk bed with her occupying the top bunker. She often teases him.