Sekai is an outwardly cheerful girl who cares deeply for her friends and seemingly helps Makoto out with Kotonoha only for fun. She often berates Makoto every time he does something inappropriate to a girl. But it's revealed she's very emotional and can spend days crying in her room. She is, to a slight extent, worldly wise, as demonstrated by her ability to give valuable advice to both Makoto and Kotonoha when their relationship gets rocky. However, this insight fails her when she is involved.