A Springtime with Ninjas (花と忍び, Hana to Shinobi) is a manga by Narumi Hasegaki. It ran in the Nakayoshi magazine from August 2015 to February 2017. It is complete in four volumes. Kodansha Comics has licensed it for English release.
Benio is the heiress of the richest family in Japan, and tradition holds that she must marry the first person to kiss her. So that she can attend high school, Benio is assigned the ninja Tamaki as a bodyguard, but he turns out to be quite the player. It’s not always easy for a strong-willed rich girl and a smart-alecky ninja to get along in this romantic comedy about a pure young lady and her smoking-hot knight.
Official English site