Такахаші Ріцуко

Head teacher of class 5-2 of Doumori Elementary, Ritsuko Takahashi (Takahashi Ritsuko, 高橋律子) is considered the madonna (term for "beautiful unmarried woman") of the school. She is very serious and dedicated to her job as a teacher, but at the same time is very edgy when it comes to the unknown, in particular the spirits and yōkai the school constantly encounters. Unfortunately, her nature is a double-edged blade for Nūbē: while her beautiful exterior makes him desire her and all the things he wants to do to her, her oversensitive nature towards the supernatural makes him tease her all the time about it...and face her wrath as a result.

At the start of the series, Ritsuko-sensei is probably the last person Nūbē would ever end up with in a relationship. Every time he tried to win her heart, she would knock him away due to being too scared of his spiritual obsessions. But as the series progresses, she slowly gains the courage to face the yōkai menaces...and as a result, slowly realizes how Nūbē is helping all those in need...and even begins to appreciate what he does both for students and all those he assists. But while her feelings slowly makes her try to become closer to the male teacher, it ends up attracting scorn from Yukime, the yuki-onna who sees herself as the one who is the teacher's true love.

The love triangle between the two teachers and the spirit girl becomes a key theme in the later part of the manga, as Nūbē is forced to decide between feelings and emotions and figure out which he wants to spend his life with. Source - Wikipedia