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 dressed appropriately for her Christmas volunteer work with the Knight Hospitaller. Rumor has it that Serina, who sings carols and distributes handmade gifts, looks like an angel that has descended on Christmas... Although Serina has a heart for helping people, when it comes to Sensei, she worries for them a lot to even go so far as to stalk them to make sure nothing bad happens, and Sensei knows of this fact. This can even be considered a hobby of hers. Serina has shoulder-length pink hair with bangs and a small bun on the right side of her head. Two strands of hair frame her face. She also has pink-colored eyes. Serina's halo resembles three yellow circles of differing sizes, the medium-sized one having two fan-shaped figures which point at the smaller central circle, and the larger having two pegs that stretch out, one to the left and the other to the right, with two more fan-shaped figures on the top and bottom. Serina wears a Christmas dress that ends at her thighs, a short Christmas cape, black gloves, black tights, and white lace-up boots with fur at the top. Atop her head, she wears a red Christmas hat adorned with a black ribbon. 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". She is 16 years old, 156 cm tall, and her birthday is January 6th.