Killing My Sensei Softly(2017)

Sensei no Yasashii Koroshi Kata

After school, Sensei tutors me in secret. My classmates think we have some sort of relationship, but they've got it all wrong. Sensei is a serial killer, and I am his apprentice. "Sensei, please teach me how to murder." A dark love unfolds between a serial killer Sensei and his devoted apprentice!

(Source: Manga UP! Global)