Otone Jinnai is Enta's older sister and a P.E teacher at Sara Middle School.
She has long pigtails on either side of her head and light green eyes. Most of the time, she wears a lavender shirt underneath a white jumper.
According to Kayoko Ishikawa, she used to wear glasses.
Otone is a caring sister and person in general. She does not want Enta to spend money. In Episode 9, while hiding her pain, she comforts Kazuki and thanks him for always being by her brother's side. When Kazuki rushes to see Enta, she starts to sob.
She is first seen presenting Toi to her class. Later, she gets angry when she sees that Enta has been buying again.
Otone and Enta have a solid sibling-relationship. They do bicker sometimes but overall, it is stable.
She is the one who presented Toi to the class in Episode 1. She is surprised when Enta says that he "mixed up his package with his", asking him if Toi is his friend.
She comforts Kazuki in Episode 9, saying that "it's not his fault, that it's the fault on whoever shot Enta".