|Japanese name:||南 ハルオ|
He got beaten up by Haruka the first time they met due to a misunderstanding, with him touching her chest. Despite this, he harbors no ill feelings towards her and instead shows signs of embarrassment and indirect affection towards her, this is made evident when the eldest Minami brother talks about having a girlfriend and Natsuki immediately pictures a provocatively dressed Haruka in his mind and suffers a nose-bleed.
"Natsu" in his name probably refers to "summer."
Voiced by: Hiroyuki Yoshino