Sumi Serina is a second-year student at Trinity General School and a member of the Trinity Remedial Knights, a club that works in the school's infirmary. She is a kind-hearted girl who enjoys doing charity work, her concern for the health of those around her has earned her a good reputation, the students often say she is like a mother. Serina is a virtuous person who enjoys caring for others, and although she is not technically a nurse, she does her job quite well. Despite having a somewhat shy personality and avoiding arguments and conflicts, she is always willing to stand her ground if challenged enough. In her spare time, Serina volunteers at hospitals and helps children around the city. Her hobbies include nursing and charity work. When it comes to Sensei, Serina is deeply concerned about their well-being, to the point of obsession. She persistently complains about Sensei's bad habits and tendency to overdo things, always forcing a stern look on her face (even though her sweet personality doesn't match it). Serina feels it's her duty and has even promised to be there for Sensei whenever it is needed, insisting that she should be the one to be called in case of trouble. It always brings a smile to her face when Sensei finally accepts her care. She has a habit of checking on Sensei at random times, making unsolicited visits, even in the middle of the night. Some would consider this stalking. Somehow, Serina is able to break into any place without alerting anyone, and appears whenever Sensei is ill or injured; she doesn't like to be questioned about it. Her presence is that of a ghost. Serina is a slim girl with pink hair and eyes. Her hair is short and tied in a side ponytail. She wears her club nurse's uniform of white and soft pink. It consists of a sailor's dress with long sleeves, white stockings and a dark blue bow on her chest, which adds to the cute design. She also carries a small bag with various medical tools. Her halo is a yellow cross with a central circle, along with other smaller artifacts. For combat, Serina carries an assault rifle. Pulling the trigger fires shots, but not the kind that heals. Specifically, it's a modified Enfield L85A1, and it's equipped with a SUSAT L9A1 telescopic sight. The school's logo is printed near the grip. The colors of her gun match well with her clothes. She nicknamed it "Tactical Therapy". Her status message on MomoChat is "I'll help you get healthy". She is 16 years old, 156 cm tall, and her birthday is January 6th.