Ikenai! Runa-sensei R

The legendary manga is reborn with new art! Wataru, a lazy high school student, is visited by the earnest and slightly airheaded teacher, Runa-sensei! So that Wataru can become a respectable adult, she gently starts giving him naughty private lessons!

(Source: Comic-Days)

Note: This is a remake of the 1986 original "Ikenai! Runa-sensei" manga