Shisan Meihua

Thirteen is a mysterious masked assassin, anti-hero, and the thirteenth daughter of the Plum Blossom swordsman.

Having been trained as a cold-blooded assassin, Thirteen is first seen as a detached and cool headed person but also prideful of her skills. When her mask is broken, it shows an easily flustered young woman who seems to have some troubles to completely disregard her feelings of rights and wrongs. Seven happens to develop a crush on her after their second encounter, and tends to hit on her. When Seven hits on her (which is during most of their interactions), she tends to act like a tsundere towards him.

She also developed feelings for Seven as shown at the end of season 2 when she was seen waiting by the ocean with a dress she bought herself and the bag with the swimsuit he bought her.