Ikenai! Luna-sensei(1986)

Ikenai! Luna-sensei

The second-year junior-high boy Wataru Kamiya hates studying. When his father is transferred overseas, a college student, Luna Hazuki, comes to live with him as a caretaker. Luna, who is also a part-time cram-school teacher, tries to get Wataru into cram-school but he is resistant. Struggling to get Wataru to change his attitude toward life, Luna tries a sexy strategy to get Wataru's attention!

(Source: Kodansha, translated)