The Tale of a High School Ninja: Let's Kick Ass! (Webtoon)

Kohana is coerced into participating in "sexual training" by Tora, her childhood friend. Tora convinces her that it is a prerequisite to being assigned to a mission where she can act as the lover of her cherished master. As Tora's requests become more insistent, can Kohana resist? The answer is no.